U.S. patent application number 14/695004 was filed with the patent office on 2015-11-12 for triggered pacing system.
The applicant listed for this patent is Medtronic, Inc.. Invention is credited to James K. Carney, Can Cinbis, Jonathan L Kuhn.
Application Number | 20150321011 14/695004 |
Document ID | / |
Family ID | 54366907 |
Filed Date | 2015-11-12 |
United States Patent
Application |
20150321011 |
Kind Code |
A1 |
Carney; James K. ; et
al. |
November 12, 2015 |
TRIGGERED PACING SYSTEM
Abstract
A medical device system is configured to sense physiological
events by a first device and control a transducer to emit trigger
signals in response to the sensed physiological events. A second
device detects the trigger signals and delivers therapeutic
stimulation pulses in response to the trigger signals. The
therapeutic stimulation pulses have a combined total time duration
over the sensed physiological events that is greater than the
combined total time duration of the trigger signals.
Inventors: |
Carney; James K.;
(Roseville, MN) ; Cinbis; Can; (Salt Lake City,
UT) ; Kuhn; Jonathan L; (Ham Lake, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Medtronic, Inc. |
Minneapolis |
MN |
US |
|
|
Family ID: |
54366907 |
Appl. No.: |
14/695004 |
Filed: |
April 23, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61989302 |
May 6, 2014 |
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Current U.S.
Class: |
607/62 |
Current CPC
Class: |
A61N 1/37276 20130101;
A61N 1/37288 20130101; A61N 1/3727 20130101; A61N 1/3987 20130101;
A61N 1/36514 20130101 |
International
Class: |
A61N 1/365 20060101
A61N001/365; A61N 1/39 20060101 A61N001/39; A61N 1/362 20060101
A61N001/362 |
Claims
1. A method for controlling automated delivery of therapeutic
stimulation pulses by a medical device system, the method
comprising: sensing a plurality of physiological events by a first
device; controlling a transducer by the first device to emit a
plurality of trigger signals in response to the sensed plurality of
physiological events, the plurality of trigger signals having a
first combined total time duration over the plurality of
physiological events; detecting the plurality of trigger signals by
a second device; delivering a plurality of therapeutic stimulation
pulses by the second device in response to detecting the plurality
of trigger signals, the plurality of therapeutic stimulation pulses
having a second combined total time duration over the plurality of
physiological events that is greater than the first combined total
time duration.
2. The method of claim 1, further comprising: setting a stimulation
pulse control parameter by the first device; controlling the
transducer by the first device to emit at least one of the
plurality of trigger signals to contain stimulation pulse control
parameter information; determining by the second device a
stimulation pulse control parameter from the detected plurality of
trigger signals including the at least one of the plurality of
trigger signals containing the stimulation pulse control parameter
information; and delivering at least one of the plurality of
stimulation pulses according to the stimulation pulse control
parameter.
3. The method of claim 2, further comprising: controlling the at
least one trigger signal to contain the stimulation pulse control
parameter information by controlling at least one of a trigger
signal width, a trigger signal pulse number and a trigger signal
interpulse interval; and determining the stimulation pulse control
parameter comprises determining at least one of the trigger signal
pulse width, the trigger signal pulse number and the trigger signal
interpulse interval.
4. The method of claim 2, further comprising: performing a capture
threshold search to determine the stimulation pulse control
parameter by: controlling the transducer to emit a series of
trigger signals to control the second device to deliver a plurality
of stimulation pulses at different pulse energies; sensing by the
first device a physiological signal to detect capture by the
plurality of stimulation pulses; and determining by the first
device the lowest pulse energy that captures a target tissue in
response to the physiological signal.
5. The method of claim 1, further comprising: determining intervals
between the plurality of sensed physiological events; determining a
metric of differences between the intervals; comparing the metric
to a change threshold; and withholding a trigger signal in response
to the metric not meeting the change threshold.
6. The method of claim 1, further comprising: determining by the
second device an interval between successive ones of the plurality
of trigger signals; storing the determined interval as a trigger
interval; starting a delay time by the second device in response to
detecting one of the plurality of trigger signals; delivering a
first one of the plurality of therapeutic stimulation pulses after
the delay time expires; scheduling a next one of the plurality of
therapeutic stimulation pulses by starting the trigger interval
upon delivering the first one of the plurality of therapeutic
stimulation pulses; adjusting the next one of the plurality of
therapeutic stimulation pulses in response to detecting a next one
of the plurality of trigger signals during the trigger interval;
and delivering the next one of the plurality of therapeutic
stimulation pulses without adjustment upon expiration of the
trigger interval if the next one of the plurality of trigger
signals is not detected during the trigger interval.
7. The method of claim 6, further comprising: controlling the
transducer by the first device to emit the next one of the
plurality of trigger signals at a control time interval after a
sensed physiological event, the control time interval being set at
a targeted therapy time interval less the delay time.
8. The method of claim 1, further comprising: monitoring a
remaining voltage of a battery of the second device by a control
module of the second device; in response to the remaining battery
voltage reaching a threshold, adjusting an amplitude of the
therapeutic stimulation pulses; sensing a physiological signal by
the first device; determining by the first device that the
amplitude of the therapeutic stimulation pulses has been adjusted
in response to the physiological signal; and generating an alert
signal by the first device in response to determining that the
amplitude has been adjusted.
9. The method of claim 1, further comprising: controlling the
transducer to emit each of the plurality of trigger signals
comprising a plurality of pulses separated by respective pulse
intervals; setting a noise rejection interval during the pulse
intervals; and rejecting a detected trigger signal pulse if a pulse
is detected during the noise rejection interval.
10. The method of claim 1, further comprising: controlling the
transducer to emit first ones of the plurality of trigger signals
with a first trigger signal parameter and second ones of the
plurality of trigger signals with a second trigger signal parameter
different than the first trigger signal parameter; detecting the
first ones of the plurality of trigger signals by the second
device, the second device configured to detect the first trigger
signal parameter; and detecting the second ones of the plurality of
trigger signals by a third device configured to detect the second
trigger signal parameter and deliver therapeutic stimulation pulses
in response to detecting the second ones of the plurality of
trigger signals.
11. A medical device system for controlling automated delivery of
therapeutic stimulation pulses, comprising: a transducer for
emitting a trigger signal; a first device configured to: sense a
plurality of physiological events; and control the transducer to
produce a plurality of trigger signals in response to the sensed
plurality of physiological events, the plurality of trigger signals
having a first combined total time duration over the plurality of
physiological events; a second device configured to: detect the
plurality of trigger signals; and deliver a plurality of
therapeutic stimulation pulses in response to detecting the
plurality of trigger signals, the plurality of therapeutic
stimulation pulses having a second combined total time duration
over the plurality of physiological events that is greater than the
first combined total time duration.
12. The system of claim 11, wherein: the first device is further
configured to: set a stimulation pulse control parameter; and
control the transducer to emit at least one of the plurality of
trigger signals to contain stimulation pulse control parameter
information; and the second device is further configured to:
determine a stimulation pulse control parameter from the detected
plurality of trigger signals including the at least one of the
plurality of trigger signals containing the stimulation pulse
control parameter information; and deliver at least one of the
plurality of stimulation pulses according to the stimulation pulse
control parameter.
13. The system of claim 12, wherein: the first device is configured
to control the at least one trigger signal to contain the
stimulation pulse control parameter information by controlling at
least one of a trigger signal width, a trigger signal pulse number
and a trigger signal interpulse interval; and the second device is
configured to determine the stimulation pulse control parameter by
determining at least one of the trigger signal pulse width, the
trigger signal pulse number and the trigger signal interpulse
interval.
14. The system of claim 12, wherein: the first device and the
second device are configured to perform a capture threshold search
to determine the stimulation pulse control parameter by:
controlling the transducer by the first device to emit a series of
trigger signals to control the second device to deliver a plurality
of stimulation pulses at different pulse energies; sensing by the
first device a physiological signal to detect capture by the
plurality of stimulation pulses; and determining by the first
device the lowest pulse energy that captures a target tissue in
response to the physiological signal.
15. The system of claim 11, wherein: the first device is further
configured to determine intervals between the plurality of sensed
physiological events; determine a metric of differences between the
intervals; compare the metric to a change threshold; and control
the transducer to withhold a trigger signal in response to the
metric not meeting the change threshold.
16. The system of claim 11, wherein the second device is further
configured to: determine an interval between successive ones of the
plurality of trigger signals; store the determined interval as a
trigger interval; start a delay time in response to detecting one
of the plurality of trigger signals; deliver a first one of the
plurality of therapeutic stimulation pulses after the delay time
expires; schedule a next one of the plurality of therapeutic
stimulation pulses by starting the trigger interval upon delivering
the first one of the plurality of therapeutic stimulation pulses;
adjust the next one of the plurality of therapeutic stimulation
pulses in response to detecting a next one of the plurality of
trigger signals during the trigger interval; and deliver the next
one of the plurality of therapeutic stimulation pulses without
adjustment upon expiration of the trigger interval if the next one
of the plurality of trigger signals is not detected during the
trigger interval.
17. The system of claim 16, wherein the first device is further
configured to control the transducer to emit the next one of the
plurality of trigger signals at a control time interval after a
sensed physiological event, the control time interval being set at
a targeted therapy time interval less the delay time.
18. The system of claim 1, wherein: the second device comprises a
control module and a battery coupled to the control module, the
control module configured to: monitor a remaining voltage of the
battery; adjust an amplitude of at least a portion of the
therapeutic stimulation pulses in response to the remaining battery
voltage reaching a threshold; the first device configured to: sense
a physiological signal; determine that the amplitude of the
plurality of the therapeutic stimulation pulses has been adjusted
in response to the physiological signal; and generate an alert
signal in response to determining that the amplitude has been
adjusted.
19. The system of claim 11, wherein: the first device is configured
to: control the transducer to emit each of the plurality of trigger
signals comprising a plurality of pulses separated by respective
pulse intervals; the second device is configured to: set a noise
rejection interval during each of the pulse intervals; and reject a
detected trigger signal pulse if the detected trigger signal pulse
is detected during the noise rejection interval.
20. The system of claim 11, further comprising a third device,
wherein: the first device is configured to: control the transducer
to emit first ones of the plurality of trigger signals with a first
trigger signal parameter and second ones of the plurality of
trigger signals with a second trigger signal parameter different
than the first trigger signal parameter; the second device is
configured to detect the first ones of the plurality of trigger
signals by detecting trigger signals of the plurality of trigger
signals having the first trigger signal parameter: and the third
device is configured to: detect the second ones of the plurality of
trigger signals by detecting trigger signals of the plurality of
trigger signals having the second trigger signal parameter; and
deliver therapeutic stimulation pulses in response to detecting the
second ones of the plurality of trigger signals.
21. A non-transitory, computer-readable storage medium storing a
set of instructions that, when executed by a processor of an
implantable medical device system, cause the system to: sense a
plurality of physiological events by a first device; control a
transducer by the first device to emit a plurality of trigger
signals in response to the sensed plurality of physiological
events, the plurality of trigger signals having a first combined
total time duration over the plurality of physiological events;
detecting the plurality of trigger signals by a second device;
delivering a plurality of therapeutic stimulation pulses by the
second device in response to detecting the plurality of trigger
signals, the plurality of therapeutic stimulation pulses having a
second combined total time duration over the plurality of
physiological events that is greater than the first combined total
time duration.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Pat. Application
No. 61/989,302 filed provisionally on May 6, 2014 and incorporated
herein by reference in its entirety. This application also
cross-references U.S. Pat. Application No. 61/989,114 and U.S. Pat.
Application No. 61/989,123, filed provisionally on May 6, 2014; and
U.S. patent application Ser. No. ______ (Atty. Docket No.
C00007389.USU2) and U.S. patent application. Ser. No. ______ (Atty.
Docket No. C00007012.USU2), filed on even date herewith, all of
which are incorporated herein by reference in their entirety.
TECHNICAL FIELD
[0002] The disclosure relates to an implantable medical device
system and associated method for delivering therapeutic stimulation
pulses using a triggered therapy delivery device.
BACKGROUND
[0003] Implantable pacemakers and cardioverter defibrillators
(ICDs) are available for delivering electrical stimulation
therapies to a patient's heart, such as bradycardia pacing, cardiac
resynchronization therapy (CRT), anti-tachycardia pacing and
cardioversion/defibrillation shocks. Medical device technology
advancement has led toward smaller and smaller implantable devices.
Recently, leadless intracardiac pacemakers have been introduced
which can be implanted directly in a heart chamber. Elimination of
transvenous, intracardiac leads has several advantages. For
example, complications due to infection associated with a lead
extending from a subcutaneous pacemaker pocket transvenously into
the heart can be eliminated. Other complications such as
"twiddler's syndrome", lead fracture or poor connection of the lead
to the pacemaker are eliminated in the use of a leadless,
intracardiac pacemaker.
[0004] New challenges arise, however, in controlling an
intracardiac pacemaker to deliver pacing pulses in synchrony with
paced or sensed events occurring in other heart chambers. Cardiac
resynchronization therapy (CRT) is an example of a pacing therapy
that includes delivering pacing pulses in a heart chamber at a
predetermined time interval after a sensed or paced event in
another heart chamber. CRT is a treatment for heart failure
patients in whom one or more heart chambers are electrically paced
to restore or improve heart chamber synchrony. Improved heart
chamber synchrony is expected to alleviate symptoms of heart
failure. Achieving a positive clinical benefit from CRT, however,
may be dependent on several therapy control parameters, such as the
timing intervals used to control pacing pulse delivery, e.g., an
atrio-ventricular (AV) interval and/or an inter-ventricular (VV)
interval. The AV interval controls the timing of ventricular pacing
pulses relative to a preceding atrial depolarization, intrinsic or
paced. The VV interval controls the timing of a pacing pulse in one
ventricle relative to a paced or intrinsic sensed event in the
other ventricle. Pacing may be delivered in the right ventricle
(RV) and/or the left ventricle (LV) to restore ventricular
synchrony.
SUMMARY
[0005] In general, the disclosure is directed to an implantable
medical device (IMD) system including a therapy delivery device and
a sensing device and an associated method for triggering the
therapy delivery device to deliver therapy. The sensing device
senses a physiological signal to determine a need for therapy and
generates a control signal passed to a trigger signal emitting
device when therapy delivery by the therapy delivery device is
required. The trigger signal emitting device emits a trigger signal
that is detected by the therapy delivery device. In response to
detecting the trigger signal, the therapy delivery device delivers
at least a portion of a therapy.
[0006] In one example, the disclosure provides a method for
controlling automated delivery of therapeutic stimulation pulses by
a medical device system. The method comprises sensing a plurality
of physiological events by a first device and controlling a
transducer by the first device to emit a plurality of trigger
signals in response to the sensed plurality of physiological
events. The plurality of trigger signals have a first combined
total time duration over the plurality of physiological events. The
method further comprises detecting the plurality of trigger signals
by a second device and delivering a plurality of therapeutic
stimulation pulses by the second device in response to detecting
the plurality of trigger signals. The plurality of therapeutic
stimulation pulses have a second combined total time duration over
the plurality of physiological events that is greater than the
first combined total time duration.
[0007] In another example, the disclosure provides an implantable
medical device (IMD) system for controlling automated delivery of
therapeutic stimulation pulses.
[0008] The system comprises a transducer for emitting a trigger
signal, a first device configured to sense a plurality of
physiological events and control the transducer to produce a
plurality of trigger signals in response to the sensed plurality of
physiological events. The plurality of trigger signals have a first
combined total time duration over the plurality of physiological
events. The system further includes a second device configured to
detect the plurality of trigger signals and deliver a plurality of
therapeutic stimulation pulses in response to detecting the
plurality of trigger signals. The plurality of therapeutic
stimulation pulses have a second combined total time duration over
the plurality of physiological events that is greater than the
first combined total time duration.
[0009] In yet another example, the disclosure provides a
non-transitory, computer-readable storage medium storing a set of
instructions that, when executed by a processor of an implantable
medical device system, cause the system to sense a plurality of
physiological events by a first device and control a transducer to
emit a plurality of trigger signals in response to the sensed
plurality of physiological events. The plurality of trigger signals
having a first combined total time duration over the plurality of
physiological events. The executed instructions further cause the
system to detect the plurality of trigger signals by a second
device and deliver a plurality of therapeutic stimulation pulses by
the second device in response to detecting the plurality of trigger
signals. The plurality of therapeutic stimulation pulses have a
second combined total time duration over the plurality of
physiological events that is greater than the first combined total
time duration.
[0010] This summary is intended to provide an overview of the
subject matter described in this disclosure. It is not intended to
provide an exclusive or exhaustive explanation of the apparatus and
methods described in detail within the accompanying drawings and
description below. Further details of one or more examples are set
forth in the accompanying drawings and the description below.
BRIEF DESCRIPTION OF DRAWINGS
[0011] FIG. 1 is a conceptual diagram of an IMD system in which a
triggered therapy delivery device may be implemented.
[0012] FIG. 2A is a conceptual diagram illustrating an implantable
medical device (IMD) system that may be used to sense cardiac
electrical signals and provide therapy to a patient.
[0013] FIG. 2B is a sectional view of the patient's anatomy
depicting an alternative configuration of system 10 of FIG. 2A.
[0014] FIG. 3A is a conceptual diagram illustrating an IMD system
according to an alternative example.
[0015] FIG. 3B is a conceptual diagram illustrating an IMD system
including multiple therapy delivery devices.
[0016] FIG. 3C is a conceptual diagram illustrating an IMD system
having an alternative sensing device.
[0017] FIG. 4 is a functional block diagram of electronic circuitry
that is included in one embodiment of the ICD shown in FIGS. 2A, 2B
and 3.
[0018] FIG. 5 is a conceptual diagram of a triggered pacemaker.
[0019] FIG. 6 is a functional block diagram of a triggered
pacemaker according to one example.
[0020] FIG. 7 is a block diagram of one example of a receiver
included in a triggered pacemaker for detecting trigger
signals.
[0021] FIG. 8 is a plot of a rectified and filtered voltage signal
provided to a comparator for detecting a trigger signal.
[0022] FIG. 9 is a flow chart of a method for controlling
therapeutic stimulation pulses delivered by an implantable medical
device system.
[0023] FIG. 10 is a flow chart of a method for controlling
triggered therapeutic stimulation pulses according to another
example.
[0024] FIG. 11 is a timing diagram of a trigger signal and
resulting pacing pulse according to one example.
[0025] FIG. 12 is a timing diagram of an alternative method for
controlling a pacing pulse parameter using a trigger signal.
[0026] FIG. 13 is a timing diagram illustrating another example
method for controlling pacing pulse delivery using trigger
signals.
[0027] FIG. 14 is a timing diagram of another method for
controlling pacing pulses using a trigger signal.
[0028] FIG. 15 is a timing diagram of a trigger signal.
[0029] FIG. 16 is a flow chart of a method for setting a pacing
pulse width by performing a pacing threshold search in a triggered
pacemaker system according to one example.
[0030] FIG. 17 is a flow chart of a method for providing a
pacemaker battery alert signal when the pacemaker battery reaches a
threshold voltage level.
[0031] FIG. 18 is a flow chart of a method for controlling a
triggered pacemaker using less than a 1:1 rate ratio of trigger
signals to pacing pulses.
[0032] FIG. 19 is a timing diagram depicting one method for
determining an interval change metric and controlling pacing pulses
delivered by a triggered pacemaker.
[0033] FIG. 20 is a timing diagram illustrating an example method
for controlling triggered and non-triggered pacing pulses using a
delay time.
[0034] FIG. 21 is a timing diagram depicting an example method for
determining an interval change metric and controlling pacing pulses
delivered by a triggered pacemaker during a decreasing heart
rate.
DETAILED DESCRIPTION
[0035] IMD systems and associated techniques are disclosed herein
for sensing physiological signals using a sensing device implanted
at one location and triggering a therapy delivery device to deliver
an automatic therapy to a targeted patient tissue at a second
location. A trigger signal is initiated by the sensing device and
detected by a transducer included in the therapy delivery device.
Automatic therapy delivery is achieved by the separate sensing and
therapy delivery devices without requiring the two devices to be
physically connected to each other. Among other things, elimination
of the physical connection between the sensing and therapy delivery
components of an IMD system enables minimally invasive implant
procedures to be used, down-sizing of IMD system components and
power supply, and/or elimination of some components such as medical
leads, sensing capability in the therapy delivery device, and a
radio frequency (RF) transmitter in the therapy delivery
device.
[0036] The trigger signal is a command, which is generated by and
sent from a sensing device to a therapy delivery device via an
emitting device to trigger the delivery of therapy by the therapy
delivery device upon detection of the trigger signal. As used
herein, a "trigger signal" is a signal emitted by a transducer when
an electrical signal is applied to the transducer. Examples of a
trigger signal include an acoustical signal, e.g., sound waves
having a frequency in the ultrasonic range produced an acoustical
transducer. Another example of a trigger signal is an optical
signal produced by a light emitting diode (LED), vertical cavity
surface emitting laser (VCSEL) or other optical transducer. In some
systems, an RF signal emitted by an RF antenna is the trigger
signal that is detected by the therapy delivery device and causes
the therapy delivery device to deliver therapy.
[0037] A "triggered therapy delivery device" as used herein is a
device that is triggered by the trigger signal to deliver a therapy
to a targeted patient tissue. In the illustrative embodiments
described herein, the therapy is an electrical stimulation therapy,
such as cardiac pacing pulses, though other types of therapy, such
as drug delivery, are contemplated. The triggered therapy delivery
device includes a transducer that produces an electrical signal in
response to being subjected to the trigger signal. The electrical
signal is compared to a trigger signal detection threshold and
causes the therapy delivery device to deliver a therapeutic
stimulation pulse to a targeted tissue of the patient when the
detection threshold is exceeded. The "triggered therapy delivery
device" as disclosed herein, therefore, is not making a decision to
deliver therapy based on sensing and processing of a physiological
signal using a transducer such as a pressure transducer, optical
transducer, electrode or other transducer that produces a
time-varying signal waveform (e.g., ECG, blood pressure, etc.)
correlated to a physiological condition or physiological events.
The decision to deliver therapy is made by a sensing device that is
controlling the transducer that emits the trigger signal. The
sensing device and the therapy delivery device need not be in wired
connection with each other.
[0038] FIG. 1 is a conceptual diagram of an IMD system 2 in which a
triggered therapy delivery device may be implemented. System 2
includes a sensing device 4, a trigger signal emitting device 5,
and a therapy delivery device 6. Sensing device 4 is capable of
sensing a physiological signal for determining when a therapy is
needed. Sensing device 4 may or may not be capable of delivering a
therapy directly to the patient. Sensing device 4 is at least
capable of sensing a physiological signal, determining need for
therapy based on the physiological signal, and producing a control
signal 3 passed to emitting device 5. In various examples, sensing
device 4 may be a pacemaker, ICD, ECG monitor, hemodynamic monitor,
neurostimulator, drug pump, or other IMD.
[0039] Sensing device 4 is in wired or wireless communication with
trigger signal emitting device 5. Sensing device 4 sends a control
signal 3 to emitting device 5 to cause emitting device 5 to emit a
trigger signal 7, shown as a directionally focused signal in FIG.
1. In other embodiments, trigger signal 7 may be multi-directional
(e.g., non-focused).
[0040] In the diagram, emitting device 5 is shown as a separate
device from sensing device 4, however in some examples emitting
device 5 is incorporated in sensing device 4. In some applications,
sensing device 4 incorporating emitting device 5 may be implanted
(or located externally) at a location that is within a trigger
signal receiving range of therapy delivery device 6. In other
applications, the physical locations of sensing device 4 and
therapy delivery device 6 may be too far apart or separated by
highly reflective tissues or attenuating structures that would
prohibit reliable reception of a trigger signal by therapy delivery
device 6. In these situations, the emitting device 5 is located at
a spaced apart location from sensing device 4 and positioned to
reliably transmit a trigger signal to therapy delivery device
6.
[0041] In various embodiments, sensing device 4 may sense any
physiological signal or combination of physiological signals used
in a particular application for determining a need for therapy.
Such signals may include, but are not limited to, an electrical
signal such as an ECG (electrocardiogram), EGM (cardiac
electrogram), EMG (electromyogram), or EEG (electroencephalogram)
or nerve action potentials. Additionally or alternatively, sensing
device 4 may be configured to sense a mechanical or chemical
physiological signal that may include, without limitation, a blood
or other pressure signal, an optical signal such as an optical
signal used to determine blood or tissue oxygen saturation, an
acoustical signal such as heart sounds, an activity signal, or a
posture signal.
[0042] The physiological signals may be used to determine a need
for therapy and for controlling the time that therapy delivery
device 6 is triggered to deliver therapy relative to sensed
physiological events. As such, sensing device 4 is configured to
determine a time that therapy is needed according to programmed
therapy delivery algorithms and therapy delivery control parameters
for a given application. Sensing device 4 controls the timing of
therapy delivery by therapy delivery device 6 via trigger signal
emitting device 5.
[0043] When sensing device 4 determines that it is time for a
therapy to be delivered, control signal 3 is passed to signal
emitting device 5. Emitting device 5 may be physically coupled to
sensing device 4 by a medical lead for passing the control signal
as an electrical signal to emitting device 5. Alternatively, the
control signal 3 is a communication signal transmitted wirelessly
to emitting device 5, from sensing device 4, such as a radio
frequency (RF) command signal that causes emitting device 5 to emit
a trigger signal 7.
[0044] Therapy delivery device 6 includes a trigger signal receiver
8, which includes a transducer that receives the trigger signal 7
and coverts it to an electrical signal. The electrical signal is
compared to a threshold to detect the trigger signal 7. In response
to detecting the trigger signal 7, therapy delivery device 6
delivers a therapy, such as one or more electrical stimulation
pulses.
[0045] In some embodiments, the trigger signal 7 is an "acoustical
trigger signal" which refers to a vibrational sound signal produced
by an acoustical transducer in the emitting device 5 and is
received by transducer 8 implemented as an acoustical transducer in
the therapy delivery device 6. The acoustical trigger signal is not
a sensed physiological signal that is produced, for example, by
sound vibrations of the patient's heart, muscle, lungs, or other
moving body part acting on a transducer. The acoustical trigger
signal is generated by emitting device 5 when an electrical control
signal 3, such as a logic signal, is produced by the circuitry of
the sensing device 4. The electrical control signal 3 may be
generated based on physiological signals, including physiological
acoustical signals, sensed by the sensing device. The acoustical
trigger signal itself, however, is originated by a device-generated
electrical control signal 3 produced by sensing device 4 to
activate the transducer of emitting device 5. The acoustical
trigger signal 7 is not a signal produced by physiological body or
vibration acting directly on the transducer 8 configured to detect
the trigger signal.
[0046] In other embodiments, the trigger signal 7 is an "optical
trigger signal" which refers to a light signal produced by an
optical transducer in the emitting device 5 and is received by a
transducer 8 implemented as an optical transducer in the therapy
delivery device 6. The optical trigger signal is not a sensed
physiological signal that is produced, for example, by sensing
remitted light from a patient's body tissue or blood for
determining a physiological parameter such as tissue color, oxygen
saturation, hemoglobin concentration, or other chromophore
concentration. The optical trigger signal is generated when
electrical control signal 3, such as a logic signal, is produced by
the circuitry of the sensing device 4. The electrical control
signal 3 is generated based on physiological signals that are
sensed by the sensing device 4, which may include physiological
optical signals. The optical trigger signal itself is originated by
a device-generated electrical control signal 3 activating the
emitting device transducer. The optical trigger signal 7 is not a
signal produced by measuring light attenuation by body tissue or
blood using the transducer 8. Rather, transducer 8 is configured to
detect the device-generated trigger signal 7 but not a
physiological signal.
[0047] Other types of trigger signals are contemplated including
radio frequency (RF) signals that are emitted by a transmitting
antenna of the emitting device 5 and received by a receiving
antenna in the therapy delivery device 6. The therapy delivery
device 6, however, may not include a standard RF transceiver for
high fidelity wireless communication. For example, therapy delivery
device 6 may include an antenna, a rectifier and filter and a
digital comparator for receiving and detecting trigger signal 7
(generated as an RF signal in this example) without
amplification.
[0048] Therapy delivery device 6 is generally a miniaturized device
that is adapted for implantation at a targeted therapy delivery
site. In some applications, the target therapy delivery site
requires a minimized device size in order to avoid complications,
minimize patient discomfort, and/or facilitate minimally invasive
implantation procedures. As such, therapy delivery device 6 may
have reduced functionality for sensing physiological signals,
collecting and storing data, radio frequency or other
bi-directional, high fidelity telemetry communication, or other
functions that may normally be present in a pacemaker, ICD,
neurostimulator or other type of IMD configured to automatically
deliver a therapy to a patient.
[0049] For example, therapy delivery device 6 may be a
transcatheter pulse generator having electrodes positioned along
the housing of the device. In some examples, a short lead carrying
one or more electrodes may extend from device 6. In the
illustrative embodiments described in greater detail below, the
therapy delivery device 6 is a transcatheter, intracardiac
pacemaker that is triggered by a signal from emitting device 5 to
deliver one or more cardiac pacing pulses. As used herein, a
"transcatheter" pacemaker or other transcatheter device is a device
that can be implanted at a target location via a catheter or other
elongated, tubular delivery tool to advance the device to a target
location without necessarily having direct line of sight at the
target location. Therapy delivery device 6 is not limited to being
a cardiac pacemaker. Device 6 may be embodied as other types of
electrical stimulation therapy delivery devices, such as devices
configured for delivering electrical stimulation to any excitable
tissue, including the central nervous system, peripheral nervous
system, smooth muscle tissue and/or skeletal muscle tissue.
[0050] Furthermore, it is recognized that triggered therapy
delivery device 6 is not limited to an electrical stimulation
therapy delivery device. In alternative embodiments, therapy
delivery device 6 may be configured to deliver other types of
therapies using mechanical, optical, pharmaceutical or other
therapeutic means. For example, therapy delivery device 6 may be a
fluid delivery device for delivering a drug or biological
agent.
[0051] FIG. 2A is a conceptual diagram illustrating an implantable
medical device (IMD) system 10 that may be used to sense cardiac
electrical signals in patient 12 and provide therapy to heart 26.
IMD system 10 includes an intracardiac pacemaker 100 and a sensing
device embodied as an ICD 14 coupled to an extravascular lead 16.
ICD 14 is implanted subcutaneously on the left side of patient 12.
Defibrillation lead 16 includes a defibrillation electrode 24,
which may be an elongated coil electrode, a pair of sensing
electrodes 28 and 30, illustrated as ring electrodes but may be or
other types of electrodes, and a trigger signal emitting device 18.
Trigger signal emitting device 18 includes a transducer that is
controlled by ICD 14 to emit trigger signals to cause pacemaker 100
to deliver one or more pacing pulses. ICD 14 is shown implanted
subcutaneously on the left side of patient 12.
[0052] Defibrillation lead 16, which is connected to ICD 14,
extends medially from ICD 14 toward sternum 22 and xiphoid process
20 of patient 12. At a location near xiphoid process 20
defibrillation lead 16 bends or turns and extends subcutaneously
superior, substantially parallel to sternum 22. Defibrillation lead
16 may be implanted such that lead 16 is over sternum 22 or offset
laterally to the left or right side of the body of sternum 22 and
may be implanted subcutaneously, e.g., between the skin and the
ribs or sternum. Defibrillation lead 16 may be implanted at other
locations or angles relative to sternum 22 or positioned further
superior or inferior depending on the location of ICD 14, position
of electrodes 24, 28, and 30 and trigger signal emitting device 18
along lead 16 and the location of pacemaker 100, or other factors.
In other instances, lead 16 may be implanted at other extravascular
locations. In one example, lead 16 may be implanted at least
partially in a substernal location or within ribcage 32, within the
thoracic cavity and within or outside the pericardium, not
necessarily in direct contact with heart 26.
[0053] Defibrillation lead 16 is placed along sternum 22 such that
a therapy vector between defibrillation electrode 24 and a second
electrode (such as a portion of the housing 15 of ICD 14 or an
electrode placed on a second lead) is substantially across one or
both ventricles of heart 26. The therapy vector may, in one
example, be viewed as a line that extends from a point on the
defibrillation electrode 24 to a point on the housing 15 (sometimes
referred to as "can electrode") of ICD 14. In another example,
defibrillation lead 16 may be placed along sternum 22 such that a
therapy vector between defibrillation electrode 24 and housing 15
of ICD 14 (or other electrode) is substantially across an atrium of
heart 26. In this case, system 10 may be used to provide atrial
therapies, such as therapies to treat atrial fibrillation.
[0054] Trigger signal emitting device 18 is positioned to establish
a trigger signal transmission pathway that does not excessively
attenuate the trigger signal transmitted from emitting device 18 to
a receiver or detector included in intracardiac pacemaker 100. For
example, the location of emitting device 18 may be selected so that
a direct pathway between emitting device 18 and pacemaker 100
avoids, as much as possible, tissues that are highly reflective,
scattering or absorbing of the type of trigger signal being used.
When lead 16 is positioned extra-thoracically, emitting device 18
may be positioned inferior to the xyphoid process 20 in a position
approximately as shown. Emitting device 18 is positioned relative
to pacemaker 100 to establish an efficient trigger signal
transmission pathway, which may be a direct or indirect pathway
that takes into account the trigger signal properties and the
transmission or attenuation properties of the surrounding and
intervening tissues for the type of trigger signal being used.
[0055] For example, the location of emitting device 18, when
embodied as an acoustical emitting device, may be selected so that
a direct acoustical pathway between emitting device 18 and
pacemaker 100 avoids lung tissue as much as possible. In another
example, the location of emitting device 18, when embodied as an
optical emitting device, may be selected so that a direct optical
pathway between emitting device 18 and pacemaker 100 avoids a large
blood volume and is directed primarily through lung tissue.
[0056] Defibrillation lead 16 may include an attachment feature 29
at or toward the distal end of lead 16. The attachment feature 29
may be a loop, link, or other attachment feature useful to aid in
implantation of lead 16 and/or for securing lead 16 to a desired
implant location. In some instances, defibrillation lead 16 may
include a fixation mechanism in addition to or instead of the
attachment feature 29. For example, defibrillation lead 16 may
include a suture sleeve or other fixation mechanism (not shown)
located proximal to electrode 30 or near emitting device 18 that is
configured to fixate lead 16 near the xiphoid process 20 or lower
sternum location. The fixation mechanism (e.g., suture sleeve or
other mechanism) may be integral to the lead or may be added by the
user prior to implantation. The fixation mechanism may be used to
stably locate emitting device 18 inferior to the xyphoid process
20, along an intercostal space, or other desired location to
prevent rotation or shifting of the emitting device 18 that may
cause trigger signal misdirection or trigger signal loss due to
interference or attenuation by body tissues.
[0057] Although ICD 14 is illustrated as being implanted near a
midaxillary line of patient 12, ICD 14 may also be implanted at
other subcutaneous locations on patient 12, such as further
posterior on the torso toward the posterior axillary line, further
anterior on the torso toward the anterior axillary line, in a
pectoral region, or at other locations of patient 12. In instances
in which ICD 14 is implanted pectorally, lead 16 would follow a
different path, e.g., across the upper chest area and inferior
along sternum 22. When the ICD 14 is implanted in the pectoral
region, the system 10 may include a second lead including a
defibrillation electrode, and optionally a trigger signal emitting
device, that extends along the left side of the patient such that
the defibrillation electrode of the second lead is located along
the left side of the patient to function as an anode or cathode of
the therapy vector for defibrillating heart 26.
[0058] ICD 14 includes a housing 15 that forms a hermetic seal that
protects components within ICD 14. The housing 15 of ICD 14 may be
formed of a conductive material, such as titanium or other
biocompatible conductive material or a combination of conductive
and non-conductive materials. Housing 15 may enclose one or more
components, including processors, memories, transmitters,
receivers, sensors, sensing circuitry, therapy circuitry and other
appropriate components (often referred to herein as modules). In
some instances, the housing 15 functions as an electrode (sometimes
referred to as a housing electrode or can electrode) that is used
in combination with one of electrodes 24, 28 and 30 to deliver a
therapy to heart 26 or to sense electrical activity of heart
26.
[0059] ICD 14 may include a connector assembly 13 (sometimes
referred to as a connector block or header) for receiving a
proximal connector (not illustrated) of lead 16. Connector assembly
13 includes electrical feedthroughs through which electrical
connections are made between conductors within defibrillation lead
16 and electronic components included within the housing 15.
Depending on the intended implant location of ICD 14, a trigger
signal emitting device may be included in connector assembly 13
and/or housing 15 in addition to or in place of the emitting device
18 carried by lead 16 for transmitting trigger signals to pacemaker
100.
[0060] Lead 16 includes a connector at the proximal end of lead 16,
such as a DF4 connector, bifurcated connector (e.g., DF-1/IS-1
connector), or other type of connector. The connector at the
proximal end of lead 16 may include a terminal pin that couples to
a port within the connector assembly 13 of ICD 14. The lead body 17
of defibrillation lead 16 may be formed from a non-conductive
material, including silicone, polyurethane, fluoropolymers,
mixtures thereof, and other appropriate materials, and shaped to
form one or more lumens within which the one or more conductors
extend. However, the techniques are not limited to such
constructions.
[0061] Defibrillation lead 16 includes elongated electrical
conductors (not illustrated) that extend within the elongated lead
body 17 from the connector on the proximal end of defibrillation
lead 16 to the respective electrodes 24, 28 and 30 and emitting
device 18. Although defibrillation lead 16 is illustrated as
including three electrodes 24, 28 and 30, defibrillation lead 16
may include more or fewer electrodes. When the connector at the
proximal end of defibrillation lead 16 is connected to connector
assembly 13, the respective conductors electrically couple to
circuitry of ICD 14, such as a therapy delivery module, a sensing
module, or trigger signal drive signal circuit, via connections in
connector assembly 13, including associated feedthroughs.
[0062] The electrical conductors transmit electrical stimulation
pulses from a therapy module within ICD 14 to one or more of
electrodes 24, 28 and 30 and transmit sensed electrical signals
from one or more of electrodes 24, 28 and 30 to the sensing module
within ICD 14. An electrical conductor extending from the proximal
lead connector to emitting device 18 conducts an electrical control
signal to emitting device 18 to cause emitting device 18 to emit a
trigger signal at appropriate times for causing intracardiac
pacemaker 100 to deliver one or more pacing pulses to heart 26.
[0063] ICD 14 may sense electrical activity of heart 26 via one or
more sensing vectors that include combinations of electrodes 28 and
30 and housing 15. For example, ICD 14 may obtain cardiac
electrical signals sensed using a sensing vector between electrodes
28 and 30, between electrode 28 and the conductive housing 15,
between electrode 30 and the conductive housing 15, or any
combination thereof. In some instances, ICD 14 may even sense
cardiac electrical signals using a sensing vector that includes
defibrillation electrode 24, such as a sensing vector between
defibrillation electrode 24 and one of electrodes 28 and 30, or a
sensing vector between defibrillation electrode 24 and the housing
15 of ICD 14.
[0064] ICD 14 determines a need for pacing therapy in response to
the sensed cardiac electrical signals, which may include P-waves
and R-waves for example, and controls emitting device 18 to emit
trigger signals based on that determination. The need for pacing
pulses may be determined according to programmed single chamber,
dual chamber or multi-chamber bradycardia or CRT control parameters
or other cardiac pacing therapy parameters. ICD 14 may also analyze
the sensed electrical signals to detect tachyarrhythmia, such as
ventricular tachycardia or ventricular fibrillation, and in
response to detecting tachyarrhythmia may generate and deliver an
electrical stimulation therapy to heart 26. For example, ICD 14 may
deliver one or more defibrillation shocks via a therapy vector that
includes defibrillation electrode 24 of defibrillation lead 16 and
the housing 15.
[0065] Electrodes 24, 28, 30 and housing 50 may be used for sensing
ECG signals for use in controlling the timing of an R-wave
synchronized shock delivered by ICD 14 and for controlling timing
of pacing pulses delivered by pacemaker 100. In some instances, one
or more pacing therapies may be delivered prior to or after
delivery of a defibrillation shock by ICD 14, such as
anti-tachycardia pacing (ATP) or post shock pacing. In these
instances, ICD 14 may generate and deliver pacing pulses via
therapy vectors that include electrodes 24, 28, 30 and/or housing
15. Alternatively, ICD 14 causes trigger signal emitting device 18
to emit trigger signals to cause pacemaker 100 to deliver pacing
pulses to heart 26 at appropriate times when ATP or post-shock
pacing is needed as well as when bradycardia or CRT pacing therapy
is needed.
[0066] The example ICD 14 illustrated in FIG. 2A is illustrative in
nature and should not be considered limiting of the sensing device
used in a triggered therapy delivery system and associated
techniques described in this disclosure. For instance, in addition
to sensing ECG signals, ICD 14 may include shock therapy
capabilities only without pacing therapy capabilities. In other
examples, ICD 14 may be coupled to more than one lead for sensing
ECG signals and/or sending trigger signals to pacemaker 100. In
still other examples, a sensing device may be substituted for ICD
14 that is a single chamber or dual chamber subcutaneous pacemaker
without cardioversion/defibrillation capabilities or a sensing-only
device without therapy delivery capabilities, e.g., as shown in
FIG. 3C. Any of these sensing devices may be coupled to
housing-based electrodes and/or electrodes carried by a
transvenous, intracardiac or extravascular, extracardiac lead for
sensing a cardiac electrical signal and determining appropriate
times for triggering pacemaker 100 to delivery therapy.
[0067] Pacemaker 100 is a transcatheter intracardiac pacemaker
adapted for implantation wholly within a heart chamber, e.g.,
wholly within the RV, wholly within the LV, wholly within the right
atrium (RA) or wholly within the left atrium (LA) of heart 26. In
the example of FIG. 2A, pacemaker 100 is positioned proximate to an
inner wall of the LV to provide left ventricular pacing. In other
examples, pacemaker 100 is positioned proximate to an inner wall of
the right ventricle to provide right ventricular pacing. In other
examples, pacemaker 100 may be positioned at any other location
outside or within heart 26, including epicardial locations. For
example, pacemaker 100 may be positioned outside or within the
right atrium or left atrium, e.g., to provide respective right
atrial or left atrial pacing. In other embodiments, pacemaker 100
may be embodied as therapy delivery device for delivering an
electrical stimulation therapy at another body location. Pacemaker
100 is shown as a leadless device in FIG. 2A. It is contemplated,
however that in other embodiments pacemaker 100 may be coupled to a
lead extending from pacemaker 100 to position therapy delivery
electrodes at a location spaced apart from pacemaker 100.
[0068] Depending on the implant location, pacemaker 100 may be
configured to deliver an electrical stimulation therapy to target
therapy site(s) other than the myocardium. For example, pacemaker
100 may provide atrioventricular nodal stimulation, fat pad
stimulation, vagal stimulation, or other types of neurostimulation.
In other examples, system 10 may include a plurality of pacemakers
100, e.g., to deliver electrical stimulation therapy at multiple
sites of heart 26 such as within multiple heart chambers for
multi-chamber pacing therapies.
[0069] Pacemaker 100 is capable of producing electrical stimulation
pulses delivered to heart 26 via one or more electrodes on the
outer housing of pacemaker 100. Pacemaker 100 includes a receiving
transducer for receiving a trigger signal emitted by emitting
device 18. In response to detecting the trigger signal, pacemaker
100 delivers one or more pacing pulses.
[0070] In one embodiment, pacemaker 100 includes a pulse generator
configured to deliver one or more pacing pulses upon receiving the
trigger signal from emitting device 18. Pacemaker 100 may not be
configured to sense cardiac signals. Cardiac signal sensing is
performed by ICD 14. ICD 14 senses ECG signals through lead 16 and
controls pacing delivered by pacemaker 100 via trigger signals
emitted by emitting device 18 under the control of ICD 14.
[0071] An intracardiac pacemaker 100 may or may not be configured
to sense cardiac signals. Pacemaker 100 may rely solely on a
trigger signal from emitting device 18 for controlling the timing
of pacing pulse delivery without sensing any other cardiac
electrical event signals or any other physiological signals. In
order to minimize the size of pacemaker 100, some functions such as
cardiac signal sensing and radio frequency telemetry functions may
be omitted such that pacemaker 100 includes a pulse generator with
limited memory, processing, and other functions directed to therapy
delivery.
[0072] In other embodiments, pacemaker 100 senses EGM signals in
the heart chamber in which it is implanted. Since pacemaker 100 is
positioned wholly within a heart chamber, however, the EGM signal
sensed by pacemaker 100 will be less sensitive or insensitive to
P-waves and/or R-waves occurring in other heart chambers. In past
practice, a subcutaneous pacemaker might be coupled to one or more
leads that position sense electrodes in or along multiple heart
chambers such that multiple sensing channels can be monitored. By
monitoring multiple sensing channels, coordinated pacing pulses can
be delivered to one or more heart chambers at specified time
intervals, e.g., AV or W intervals.
[0073] Since pacemaker 100 may have no or limited sensing
capabilities, pacemaker 100 may be "blinded" to intrinsic events,
such as intrinsic R-waves, occurring in the same heart chamber and
to paced or intrinsic events occurring in other heart chambers.
Delivery of CRT, dual chamber pacing, or other multi-chamber pacing
therapies may require delivering a pacing pulse at a predetermined
time interval after an event, sensed or paced, in another heart
chamber. As such, emitting device 18 provides a trigger signal to
pacemaker 100 in response to ECG signals sensed by ICD 14 to cause
pacing pulses to be delivered by pacemaker 100 at desired time
intervals relative to other heart chamber events. Pacemaker 100
(for generating pacing pulses) combined with ICD 14 (for sensing
physiological signals and making therapy delivery decisions)
provides the functionality required to deliver various therapies
that may require synchronization or coordination with cardiac
events occurring in the same or a different heart chamber without
physical connection between pacemaker 100 and ICD 14 implanted at
separate implant sites.
[0074] FIG. 2A further depicts programmer 40 in wireless
communication with ICD 14 via communication link 42. In some
examples, programmer 40 comprises a handheld computing device,
computer workstation, or networked computing device. Programmer 40
includes a user interface that presents information to and receives
input from a user. It should be noted that the user may also
interact with programmer 40 remotely via a networked computing
device.
[0075] A user, such as a physician, technician, surgeon,
electrophysiologist, other caregiver, or patient, interacts with
programmer 40 to communicate with ICD 14. For example, the user may
interact with programmer 40 to retrieve physiological or diagnostic
information from ICD 14. A user may also interact with programmer
40 to program ICD 14, e.g., select values for operational
parameters of the ICD 14, including parameters used to control
trigger signal emitting device 18 for controlling pacemaker 100. A
user may use programmer 40 to retrieve information from ICD 14
regarding the rhythm of heart 26, heart rhythm trends over time, or
arrhythmic episodes.
[0076] As indicated, ICD 14 and programmer 40 communicate via
wireless communication. Examples of communication techniques may
include low frequency or radiofrequency (RF) telemetry, but other
techniques may be used. In some examples, programmer 40 may include
a programming head that is placed proximate to the patient's body
near the ICD 14 implant site in order to improve the quality or
security of communication between ICD 14 and programmer 40.
[0077] The embodiment illustrated in FIG. 2A is an example
configuration of an IMD system 10 and should not be considered
limiting of the techniques described herein. In other embodiments,
ICD 14 may be coupled to a transvenous intracardiac lead extending
into the right ventricle (RV) for positioning RV sensing and pacing
electrodes and a defibrillation coil electrode within the RV. An
example of an RV lead that could be adapted to carry an emitting
device 18 is generally disclosed in commonly-assigned, U.S. Pat.
No. 5,545,186 (Olson, et al.). In this example, emitting device 18
may be positioned more distally than the position shown on lead 16
such that the emitting device 18 is positioned in the RV, opposite
pacemaker 100 in the LV. Emitting device 18 may then be enabled to
emit a trigger signal from the RV to the pacemaker 100 in the LV to
coordinate timing of the LV pacing pulse relative to a right atrial
event or a right ventricular event. It is contemplated that
numerous configurations of a lead-based emitting device 18 may be
conceived and emitting device 18 may be positioned along the lead
body 17 at relatively more proximal or more distal locations than
shown on lead 16 to position emitting device 18 at a desired
location relative to pacemaker 100.
[0078] FIG. 2B is a sectional view of the patient's anatomy
depicting an alternative configuration of system 10 of FIG. 2A.
Emitting device 18 is shown in a substernal position on lead 16
(not seen in the sectional view of FIG. 2B). Instead of being
positioned suprasternally, inferior to the xyphoid process,
emitting device 18 may be positioned substernally and relatively
more superior by advancing the distal end of lead 16 to a
substernal location. Emitting device 18 may be configured for
directional trigger signal emission with emitting device 18
oriented to generally direct the trigger signal toward the implant
position of pacemaker 100, e.g., along a signal pathway to
pacemaker 100 as represented by arrow 72.
[0079] Lead 16 may be placed under or below the sternum in the
mediastinum and, more particularly, in the anterior mediastinum.
The anterior mediastinum is bounded laterally by pleurae,
posteriorly by pericardium, and anteriorly by sternum. Lead 16 may
be at least partially implanted in other extra-pericardial
locations, i.e., locations in the region around, but not
necessarily in direct contact with, the outer surface of heart 26.
These other extra-pericardial locations may include in the
mediastinum but offset from sternum 22, in the superior
mediastinum, in the middle mediastinum, in the posterior
mediastinum, in the sub-xiphoid or inferior xiphoid area, near the
apex of the heart, or other location not in direct contact with
heart 26 and not subcutaneous. In other embodiments, lead 16 may
extend within the pericardium and in direct contact with heart 26.
In any of these illustrative implant locations, lead 16 may be
positioned to optimally position trigger signal emitting device 18
for reliably transmitting a trigger signal to pacemaker 100.
[0080] FIG. 3A is a conceptual diagram illustrating an IMD system
10' according to an alternative example. ICD 14 coupled to lead 16
is used to sense cardiac electrical signals in patient 12 and
provide therapy to heart 26 as described above. Intracardiac
leadless pacemaker 100 is implanted within the LV and delivers
pacing pulses to the LV in response to receiving a trigger signal.
In this embodiment, trigger signal emitting device 18 is carried by
a separate lead 60 coupled to ICD 14 and positioned
extrathoracically, e.g., along an intercostal space, to direct a
trigger signal toward pacemaker 100 through the intercostal space
and intervening muscle, blood, myocardial tissue, etc. Emitting
device 18 is capable of receiving an electrical control signal from
ICD 14 conducted along lead 60. Upon receipt of the control signal,
emitting device 18 emits a trigger signal to cause pacemaker 100 to
deliver an LV pacing pulse.
[0081] A dedicated lead 60 carrying emitting device 18 may be
provided to position emitting device 18 at an optimal location for
transmitting a trigger signal to pacemaker 100. An optimal location
is a location of emitting device 18 relative to pacemaker 100 that
allows a trigger signal to reach pacemaker 100 with adequate signal
intensity and signal-to-noise ratio that it is reliably detected by
pacemaker 100. A trigger signal path between emitting device 18 and
pacemaker 100 may include tissues that attenuate the trigger signal
through absorption, scattering or reflection of the signal. The
location of emitting device 18 is selected such that signal losses
along the path do not reduce the intensity of the trigger signal
below a threshold level that is detectable by pacemaker 100.
[0082] In some examples, emitting device 18 may have its own
battery, which may be rechargeable, such that the power required by
ICD 14 for sensing and therapy delivery functions and the power
required for trigger signal emission is distributed across two
devices and two (or more) batteries or other power sources.
[0083] Emitting device 18 may alternatively be embodied as a
leadless device capable of receiving a wireless control signal from
ICD 14 to cause trigger signal emission. For example, emitting
device 18 may include an RF receiver for receiving a wireless RF
control signal from ICD 14.
[0084] Emitting device 18 carried by a dedicated lead 60, or a
leadless emitting device, may be positioned at an optimal location
for transmitting a trigger signal to pacemaker 100 without
limitations associated with optimal positioning of electrodes 24,
28 and 30 for sensing ECG signals and delivering shock therapy. A
leadless emitting device may be implanted at a desired site without
requiring lead tunneling. The emitting device 18 may act as a relay
device for transmitting the control signal from ICD 14 to pacemaker
100 by converting the control signal to a trigger signal that is
transmitted to and detected by pacemaker 100.
[0085] Emitting device 18 may be positioned external to the ribcage
32 such that the trigger signal is directed through an intercostal
space toward heart 26. Transmission of a trigger signal along a
path through blood and muscle tissue may be more efficient than a
path through lung tissue or vice versa depending on the type of
trigger signal being emitted. The intensity or amplitude and
frequency of the trigger signal and/or other trigger signal
properties may be selected to provide efficient transmission
through the tissues along the pathway between the trigger signal
emitting device 18 and the receiving pacemaker 100.
[0086] In some examples, multiple emitting devices may be included
in systems 10 or 10'. Depending on the final implant position of
pacemaker 100 and shifting that may occur over time, pacemaker 100
may be more sensitive to a trigger signal emitted by one device
than by another device at a different location. Multiple emitting
devices positioned at different, spaced apart locations may be
selected individually or in combination by ICD 14 to emit a trigger
signal to achieve reliable trigger signal detection by pacemaker
100 using the greatest power efficiency.
[0087] Furthermore, it is contemplated that a trigger signal
emitting device can be located in the ICD 14, e.g., along its
housing 15 and/or connector assembly 13. In some embodiments, ICD
14 may be implanted relative to pacemaker 100 so that a trigger
signal may be reliably transmitted from ICD 14 to pacemaker 100.
The implant location of ICD 14 is selected to establish a
defibrillation vector between electrode 24 and ICD housing 15.
[0088] FIG. 3B is a conceptual diagram illustrating an IMD system
11 including multiple therapy delivery devices 100, 100', and
100''. In the example shown, one pacemaker 100 is shown in the LV,
pacemaker 100' is shown in the RV and pacemaker 100'' is shown in
the RA. In embodiments including multiple intracardiac pacemakers
100, 100' and 100'', the receiving transducers in each pacemaker
100, 100' and 100'' may be configured to be sensitive to different
trigger signal frequencies, signal amplitudes, signal pulse numbers
or other trigger signal characteristic. In the example shown, and
as described in conjunction with FIG. 2A, the sensing device may be
embodied as an ICD 14 that controls lead-based emitting device 18.
Emitting device 18 may be controlled to emit a trigger signal at a
first frequency, wavelength, or other signal characteristic for
triggering an RV pacemaker 100' configured to detect trigger
signals having the first frequency, wavelength or other
characteristic (and ignore other trigger signals not having the
first frequency, wavelength or other characteristic) and to emit a
second trigger signal at a second frequency, wavelength or other
characteristic for triggering an LV pacemaker 100 configured to
detect trigger signals having the second frequency, wavelength or
other characteristic. The emitting device 18 may be controlled by
ICD 14 to emit a trigger signal according to the first
characteristic to cause delivery of a triggered RV pacing pulse and
emit a second trigger signal according to the second characteristic
to trigger an LV pacing pulse at a controlled time interval
(positive or negative) relative to the triggered pace in the RV.
Similarly, RA pacemaker 100'' may be triggered to deliver a pacing
pulse in response to a third wavelength.
[0089] Alternatively, when two or more therapy delivery devices
100, 100' and 100'' are included in the IMD system 11, multiple
emitting devices 18, 18' and 18'', each configured to target a
trigger signal at one specific therapy device 100, 100' or 100''
may be used. For example, paired emitting devices 18, 18' and 18''
and therapy delivery devices 100, 100' and 100'' may be implanted
relative to each other so that each emitting device 18, 18' and
18'' is positioned and controlled to focus an emitted trigger
signal at a respective therapy delivery device 100, 100' and 100''.
To illustrate, lead-based emitting device 18 may be configured to
transmit a trigger signal to pacemaker 100' positioned in the RV, a
second lead-based emitting device 18' may be configured to transmit
a trigger signal to pacemaker 100 positioned in the LV, and a third
lead-based emitting device 18'' may be configured to emit a trigger
signal to pacemaker 100'' positioned in the RA.
[0090] Depending on the transducer used in the emitting device 18,
trigger signals may be sequentially steered or focused toward
different targeted therapy delivery devices 100, 100' and 100'' by
a single emitting device 18. For example, if an acoustic trigger
signal emitting device is used, an array of transducers may be
controlled to focus the trigger signal at one therapy delivery
device 100 and then controlled to focus the trigger signal at
another therapy delivery device 100' and so on.
[0091] In still other examples, other trigger signal parameters
besides frequency or wavelength may be used to transmit mutually
exclusive trigger signals that are recognized and detected by the
appropriate therapy delivery device 100, 100' or 100''. For
example, mutually exclusive trigger signal patterns, such as
different pulse numbers, different interpulse intervals, different
pulse widths, different rising and/or falling slope of a trigger
signal pulse or any combination thereof may be used to exclusively
trigger different therapy delivery devices 100, 100' and 100''. To
illustrate, one therapy delivery device 100 may detect a trigger
signal having more than two pulses as invalid while another therapy
delivery device 100' may require detection of a minimum of three
pulses to recognize a valid trigger signal. In another example, one
therapy delivery device 100 may detect a valid trigger signal
having a short-long-short interpulse interval pattern and another
therapy delivery device 100'' may detect a valid trigger signal as
one having a long-short-long interpulse interval pattern.
[0092] In other applications, as shown by system 10'' in FIG. 3C, a
different type of sensing device 44 may be substituted for ICD 14
that may implanted at a variety of locations that facilitate
trigger signal transmission from the sensing device 44 to pacemaker
100 without requiring a lead-based or leadless emitting device
spaced apart from the sensing device 44. The emitting device 45 may
be incorporated along the housing of the sensing device 44. Sensing
device 44 may be embodied as a sensing-only device without therapy
delivery capabilities and is shown as an ECG monitor having a pair
of housing-based electrodes 46 for sensing an ECG signal. Based on
cardiac events sensed from the ECG signal, sensing device 44
controls emitting device 45 to emit a trigger signal to cause
pacemaker 100 to deliver one or more pacing pulses.
[0093] It is recognized that a triggered therapy delivery system
including any combination and arrangement of one or more therapy
delivery devices, one or more emitting devices, and one or more
sensing devices may be conceived to meet the needs of a particular
therapeutic application based on the teachings of the present
disclosure. The systems 2, 10, 10', 11 and 10'' shown in FIGS. 1,
2A, 2B, 3A, 3B, and 3C, respectively, are intended to illustrate
various possible combinations and arrangements of a triggered
therapy delivery IMD system with no limitation intended. A therapy
delivery system employing the techniques disclosed herein may
include different combinations and arrangements of at least one
therapy delivery device, at least one sensing device and at least
one trigger signal emitting device than the combinations and
arrangements shown in the accompanying drawings.
[0094] FIG. 4 is a functional block diagram of electronic circuitry
that is included in one embodiment of ICD 14 shown in FIGS. 2A, 2B
and 3. ICD 14 includes processing and control module 80, also
referred to as "control module" 80, memory 82, therapy delivery
module 84, electrical sensing module 86, telemetry module 88, and
cardiac signal analyzer 90. A power source 98 provides power to the
circuitry of ICD 14, including each of the modules 80, 82, 84, 86,
88, 90. Power source 98 may include one or more energy storage
devices, such as one or more chargeable or non-re-chargeable
batteries.
[0095] The functional blocks shown in FIG. 4 represent
functionality that may be included in ICD 14 and may include any
discrete and/or integrated electronic circuit components that
implement analog and/or digital circuits capable of producing the
functions attributed to ICD 14 herein. For example, the modules may
include analog circuits, e.g., amplification circuits, filtering
circuits, and/or other signal conditioning circuits. The modules
may also include digital circuits, e.g., analog-to-digital
converters, combinational or sequential logic circuits, integrated
circuits, memory devices, etc. Memory 82 may include any volatile,
non-volatile, magnetic, or electrical non-transitory computer
readable storage media, such as a random access memory (RAM),
read-only memory (ROM), non-volatile RAM (NVRAM),
electrically-erasable programmable ROM (EEPROM), flash memory, or
any other memory device. Furthermore, memory 82 may include
non-transitory computer readable media storing instructions that,
when executed by one or more processing circuits, cause control
module 80 or other ICD modules to perform various functions
attributed to ICD 14. The non-transitory computer readable media
storing the instructions may include any of the media listed above,
with the sole exception being a transitory propagating signal. The
particular form of software, hardware and/or firmware employed to
implement the functionality disclosed herein will be determined
primarily by the particular system architecture employed in the IMD
system devices. Providing software, hardware, and/or firmware to
accomplish the described functionality in the context of any modern
IMD system, given the disclosure herein, is within the abilities of
one of skill in the art.
[0096] The functions attributed to the modules herein may be
embodied as one or more processors, hardware, firmware, software,
or any combination thereof. Depiction of different features as
modules is intended to highlight different functional aspects and
does not necessarily imply that such modules must be realized by
separate hardware or software components. Rather, functionality
associated with one or more modules may be performed by separate
hardware or software components, or integrated within common
hardware or software components. For example, arrhythmia detection
operations performed by cardiac signal analyzer 90 for determining
a need for therapy delivered by ICD 14 and/or pacemaker 100 may be
implemented in processing and control module 80 executing
instructions stored in memory 82.
[0097] Processing and control module 80 communicates with therapy
delivery module 84, cardiac signal analyzer 90 and electrical
sensing module 86 for sensing cardiac electrical activity,
detecting cardiac rhythms, and generating cardiac therapies in
response to sensed signals. Therapy delivery module 84 and
electrical sensing module 86 are electrically coupled to electrodes
24, 28, and 30 carried by lead 16, e.g., as shown in FIG. 2A, and
housing 15, at least a portion of which also serves as a common or
ground electrode.
[0098] Electrical sensing module 86 is coupled to electrodes 28 and
30 in order to monitor electrical activity of the patient's heart.
Electrical sensing module 86 may optionally be coupled to
electrodes 24 and 15 and enabled to selectively monitor one or more
sensing vectors selected from the available electrodes 24, 28, 30
and 15. For example, sensing module 86 may include switching
circuitry for selecting which of electrodes 24, 28, 30 and housing
15 are coupled to sense amplifiers included in sensing module 86.
Switching circuitry may include a switch array, switch matrix,
multiplexer, or any other type of switching device suitable to
selectively couple sense amplifiers to selected electrodes. A
sensing vector between electrodes 28 and 30 may be selected for
sensing an ECG signal, although it is recognized that in some
embodiments sensing vectors may be selected that utilize coil
electrode 24 and/or housing electrode 15, e.g., from electrode 28
to housing 15 or electrode 30 and housing 15.
[0099] One or more ECG signals are received by an input of sensing
module 86. Sensing module 86 includes one or more sense amplifiers
or other cardiac event detection circuitry for sensing cardiac
events, e.g., P-waves or R-waves, from the ECG signal(s). Sensing
module 86 passes sense event signals to cardiac signal analyzer 90
in response to sensing cardiac events. For example P-wave sense
event signals and R-wave sense event signals are passed to cardiac
signal analyzer 90 when the ECG signal crosses a respective P-wave
sensing threshold and R-wave sensing threshold, which may each be
auto-adjusting sensing thresholds. Bradycardia or asystole is
typically determined by a pacing escape interval timer expiring
within the timing circuit 92. In response to the pacing escape
interval expiring, a control signal 95 is passed to the trigger
signal emitting device 18. The pacing escape interval is restarted
upon a trigger signal or a sense event signal.
[0100] The control signal 95 in the illustrative examples presented
herein may be referred to as a pacing control signal because it
causes pacemaker 100 to deliver a pacing pulse to a heart chamber.
In other examples, the control signal 95 may be produced by cardiac
signal analyzer 90 to cause other types of therapy pulses to be
delivered by pacemaker 100 (or another therapy delivery device).
For example control signal 95 may be produced to cause pacemaker
100 or another therapy delivery device to deliver an ATP pulse, a
vagal nerve stimulation pulse, or other type of electrical
stimulation pulse.
[0101] The control signal 95 is an electrical signal that is passed
to emitting device 18 along lead 16 or 60 (or another lead carrying
emitting device 18) when emitting device 18 is coupled to ICD 14 in
a wired connection. The control signal 95 is alternatively a
wireless telemetry signal that is transmitted via telemetry module
88, to emitting device 18. Emitting device 18 may be carried by a
lead but configured to wirelessly receive a control signal 95 from
telemetry module 88. Alternatively, the emitting device 18 is not a
lead-based emitting device and receives control signal 95
wirelessly, e.g., as an RF telemetry signal, from telemetry module
88. It is understood that in some embodiments, drive signal circuit
34 may be included within the housing 15 of ICD 14 and coupled to
transducer 36 located external to housing 15.
[0102] Trigger signal emitting device 18 includes a drive signal
circuit 34 that receives the control signal 95, either as a wired
electrical signal or a wireless signal from telemetry module 88.
Drive signal circuit 34 passes an electrical signal to transducer
36 to enable transducer 36 to emit the trigger signal. Transducer
36 may be an optical transducer or an acoustical transducer in
various examples. In other examples, the drive signal circuit 34 is
coupled to an antenna for transmitting the trigger signal as an RF
signal.
[0103] The trigger signal is received and detected by pacemaker 100
causing pacemaker 100 to deliver one or more pacing pulses to the
patient's heart. In some examples, the trigger signal is generated
according to predetermined frequency, amplitude, duration and other
characteristics that are not intentionally varied by emitting
device 18 under the control signal 95. In other words, the trigger
signal merely signals pacemaker 100 to deliver therapy without any
information relating to how many pacing pulses, what pulse
amplitude or pulse width or other pacing pulse control parameters.
Pacemaker 100 is programmed to deliver a predetermined number of
pacing pulses according to predefined pulse control parameters when
the trigger signal is detected.
[0104] Alternatively, control signal 95 may include encoded pacing
pulse control information. The control signal 95 generated by drive
circuit 34 may cause transducer 36 to emit a trigger signal
according to a frequency, duration, amplitude or other
intentionally varied characteristics of the trigger signal to
include pacing pulse control parameter information. As described
below, a parameter of the trigger signal emitted by transducer 36
may be controllably varied by control signal 95 and drive circuit
34 to cause pacemaker 100 to adjust a pacing pulse control
parameter such as pacing pulse width, pulse number, etc. Trigger
signal parameters that may be varied under the control of signal 95
and drive circuit 34 include, without limitation, trigger signal
amplitude, signal frequency, pulse width, pulse number and
interpulse interval.
[0105] Transducer 36 may be embodied as one or more transducers
configured to emit sound or light, for example, upon receiving a
drive signal from circuit 34. Transducer 36 may include any
combination of one or more of a ceramic piezoelectric crystal, a
polymer piezoelectric crystal, capacitive micromachined ultrasonic
transducer (CMUT), piezoelectric micromachined ultrasonic
transducer (PMUT), or other ultrasonic transducer, a light emitting
diode (LED), a vertical cavity surface emitting laser (VCSEL) or
other light source having a high quantum efficiency at a selected
light wavelength. Transducer 36 may include multiple transducers
arranged in an array and/or configured to emit signals in multiple
directions from emitting device 18 to promote reception of the
trigger signal by pacemaker 100 despite shifting, rotation or other
changes of the relative orientations of emitting device 18 and
pacemaker 100 with respect to each other. The multiple transducers
may be selectable by drive circuit 34 such that a single one or
combination of transducers producing the best signal-to-noise ratio
at the pacemaker receiving transducer is selected.
[0106] In one example, transducer 36 may include multiple acoustic
transducers activated by drive signal circuit 34 to emit sound
waves that constructively interfere to improve the efficiency of
acoustical signal transmission. Emitting device 18 is shown as a
single device but may be implemented as more than one emitting
device such that transmission of the trigger signal is distributed
over two or more emitting devices. When two or more emitting
devices are used, emitting device 18 may include one or more
lead-based emitting devices, one or more leadless emitting devices,
and/or one or more emitting devices incorporated in ICD 14. Two or
more emitting devices may be activated synchronously to produce
ultrasound waves that superimpose at the receiver of pacemaker 100
to increase transmission efficiency and/or improve signal
reception. A phased array of transducers that can be independently
pulsed to emit sound can be used to focus the acoustical signal
toward the intended receiving transducer in pacemaker 100. When
multiple pacemakers 100 or other therapy delivery devices are
included, a phased array of transducers included in transducer 36
may be controlled by drive signal circuit 34 to pulse the
transducers in a programmed time relationship to focus the trigger
signal on the receiver of an intended therapy delivery device.
[0107] Transducer 36 may include multiple transducers having
different properties for emitting different frequencies of sound,
light or RF signal. The different transducers are selectable by
drive circuit 34 to enable transmission of different frequencies of
trigger signals. For example, different frequencies or different
patterns of amplitude, frequency, pulse number, etc. may be emitted
for triggering different responses by pacemaker 100 or for
triggering different intracardiac pacemakers when multiple
pacemakers are implanted. As indicated above, different trigger
signals may be used to cause pacemaker 100 to deliver pacing pulses
according to different pacing pulse control parameters, such as
different pulse shape, pulse amplitude, pulse width, pulse rate or
pulse number.
[0108] The transducer 36 is configured to emit a trigger signal at
an amplitude and frequency that is detectable by a receiving
transducer of pacemaker 100, after attenuation by body tissues
along the pathway between the transducer 36 and the pacemaker 100.
In one example, transducer 36 is configured to emit sounds in the
range of approximately 40 kHz to over 1 MHz. An optical trigger
signal may be emitted with a wavelength greater than approximately
1000 nm. An RF signal can be radiated from an antenna at
frequencies between 400 MHz and 3 GHz. The frequency of the trigger
signal is selected in part based on the types and thicknesses of
body tissues encountered along the signal pathway.
[0109] Timing circuit 92 may generate control signal 95 to trigger
pacemaker 100 to provide bradycardia pacing, anti-tachycardia
pacing, cardiac resynchronization therapy, AV nodal stimulation, or
other pacing therapies according to pacing algorithms and timing
intervals stored in memory 82. Bradycardia pacing may be delivered
by pacemaker 100 temporarily to maintain cardiac output after
delivery of a cardioversion-defibrillation shock by ICD 14 as the
heart recovers back to normal function post-shock.
[0110] Cardiac signal analyzer 90 includes a tachyarrhythmia
detector 94 for detecting and discriminating supraventricular
tachycardia (SVT), ventricular tachycardia (VT) and ventricular
fibrillation (VF). Some aspects of sensing and processing
subcutaneous ECG signals are generally disclosed in
commonly-assigned U.S. Pat. No. 7,904,153 (Greenhut, et al.),
hereby incorporated herein by reference in its entirety. The timing
of R-wave sense event signals from sensing module 86 is used by
tachyarrhythmia detector 94 to measure R-R intervals for counting
RR intervals in different detection zones or determining a heart
rate or other rate-based measurements for detecting ventricular
tachyarrhythmia. Electrical sensing module 86 may additionally or
alternatively provide digitized ECG signals to cardiac signal
analyzer 90 for use in detecting tachyarrhythmia. Examples of ICDs
that may be adapted for use with a triggered pacemaker 100 and
operations that may be performed by tachyarrhythmia detector 94 for
detecting, discriminating and treating tachyarrhythmia are
generally disclosed in U.S. Pat. No. 7,742,812 (Ghanem, et al.),
U.S. Pat. No. 8,160,684 (Ghanem, et al.), U.S. Pat. No. 5,354,316
(Keimel); U.S. Pat. No. 6,393,316 (Gillberg et al.), U.S. Pat. No.
5,545,186 (Olson, et al.), and U.S. Pat. No. 5,855,593 (Olson, et
al.), all of which patents are incorporated herein by reference in
their entirety.
[0111] The detection algorithms are highly sensitive and specific
for the presence or absence of life threatening VT and VF. Therapy
delivery module 84 includes a HV therapy delivery module including
one or more HV output capacitors. When a malignant tachycardia is
detected the HV capacitors are charged to a pre-programmed voltage
level by a HV charging circuit. Control module 80 applies a signal
to trigger discharge of the HV capacitors upon detecting a feedback
signal from therapy delivery module 84 that the HV capacitors have
reached the voltage required to deliver a programmed shock energy.
In this way, control module 80 controls operation of the high
voltage output circuit of therapy delivery module 84 to deliver
high energy cardioversion/defibrillation shocks using coil
electrode 24 and housing electrode 15.
[0112] It should be noted that implemented arrhythmia detection
algorithms may utilize not only ECG signal analysis methods but may
also utilize supplemental sensors 96, such as tissue color, tissue
oxygenation, respiration, patient activity, heart sounds, and the
like, for contributing to a decision by processing and control
module 80 to apply or withhold a therapy. Sensors 96 may also be
used in determining the need and timing for pacing by pacemaker
100. For example, an activity sensor signal or other rate
responsive sensor signal, such as a minute ventilation signal, may
be used for determining a pacing rate meeting a patient's metabolic
demand. Timing circuit 92 produces a control signal 95 to cause
emitting device 18 to generate trigger signals that cause pacemaker
100 to deliver pacing pulses at an appropriate rate based on the
rate responsive signal. Sensors 96 may include one or more sensors
carried by a lead extending from ICD 14 or within or along housing
15 and/or connector block 13.
[0113] Telemetry module 88 includes a transceiver and antenna for
communicating with another device, such as an external programmer
40 and emitting device 18 when it is configured to receive control
signal 95 wirelessly. Under the control of control module 80,
telemetry module 88 may receive downlink telemetry from and send
uplink telemetry to programmer 40 or another external device.
Telemetry module 88 may transmit a control signal wirelessly to
emitting device 18, e.g., as an RF signal.
[0114] FIG. 5 is a conceptual diagram of pacemaker 100. Pacemaker
100 includes electrodes 162 and 164 spaced apart along the housing
150 of pacemaker 100. Electrode 164 is shown as a tip electrode
extending from a distal end 102 of pacemaker 100, and electrode 162
is shown as a ring electrode along a mid-portion of housing 150,
for example adjacent proximal end 104. In alternative embodiments,
pacemaker 100 may include two or more ring electrodes or other
types of electrodes exposed along pacemaker housing 150 for
delivering electrical stimulation to heart 26. Electrodes 162 and
164 may be, without limitation, titanium, platinum, iridium or
alloys thereof and may include a low polarizing coating, such as
titanium nitride, iridium oxide, ruthenium oxide, platinum black
among others. Electrodes 162 and 164 may be positioned at locations
along pacemaker 100 other than the locations shown.
[0115] The housing 150 includes a control electronics subassembly
152, which houses the electronics for producing stimulation pulses
and performing therapy delivery functions of pacemaker 100. As one
example, control electronics subassembly 152 may include a pulse
generator and a receiving transducer for receiving the trigger
signal from emitting device 18 and triggering the pulse generator
to deliver a pacing pulse via pacing tip electrode 164 and return
anode electrode 162 in response to the trigger signal.
[0116] Housing 150 further includes a battery subassembly 160,
which provides power to the control electronics subassembly 152.
Battery subassembly 160 may include features of the batteries
disclosed in commonly-assigned U.S. Pat. No. 8,433,409 (Johnson, et
al.) and U.S. Pat. No. 8,541,131 (Lund, et al.), both of which are
hereby incorporated by reference herein in their entirety. Housing
150 is formed from a biocompatible material, such as a stainless
steel or titanium alloy. In some examples, the housing 150 may
include an insulating coating. Examples of insulating coatings
include parylene, urethane, PEEK, or polyimide among others. The
entirety of the housing 150 may be insulated, but only electrodes
162 and 164 uninsulated. In other examples, the entirety of the
housing 150 may function as an electrode instead of providing a
localized electrode such as electrode 162. Alternatively, electrode
162 may be electrically isolated from the other portions of the
housing 150. Electrodes 162 and 164 form an anode and cathode pair
for bipolar cardiac pacing.
[0117] Pacemaker 100 may include a set of active fixation tines 166
to secure pacemaker 100 to patient tissue, e.g., by interacting
with the ventricular trabeculae. Fixation tines 166 are configured
to anchor pacemaker 100 to position electrode 164 in operative
proximity to a targeted tissue for delivering therapeutic
electrical stimulation pulses. In some embodiments, electrodes 162
and 164 are also used for sensing cardiac EGM signals, in which
case control electronics subassembly 152 includes sensing
circuitry. Numerous types of active and/or passive fixation members
may be employed for anchoring or stabilizing pacemaker 100 in an
implant position. Pacemaker 100 may include a set of active
fixation tines as disclosed in commonly-assigned, pre-grant
publication U.S. 2012/0172892 (Grubac, et al.), hereby incorporated
herein by reference in its entirety.
[0118] Pacemaker 100 may further include a delivery tool interface
158. Delivery tool interface 158 is located at the proximal end of
pacemaker 100 and is configured to connect to a delivery device,
such as a catheter, used to position pacemaker 100 at an implant
location during an implantation procedure, for example within a
heart chamber.
[0119] Pacemaker 100 includes a coupling member 180 for coupling a
trigger signal from emitting device 18 to a receiving transducer
enclosed within housing 150. For example, coupling member 180 may
be an acoustic coupling member for transferring sound waves to an
acoustic receiving transducer (not shown) enclosed within housing
150 along an inner surface of coupling member 180. In another
example, coupling member 180 may be a transparent window for
transferring light emitted by emitting device 18 to an optical
receiving transducer enclosed within housing 150 along an inner
surface of member 180.
[0120] When pacemaker 100 is advanced transvenously into a heart
chamber, the final orientation of pacemaker 100 may vary. The final
orientation of coupling member 180 relative to the patient's
anatomy, and therefore the final orientation relative to emitting
device 18 may be unknown. Furthermore, the orientation of coupling
member 180 relative to the emitting device 18 may fluctuate over
time due to shifting of either pacemaker 100 or emitting device 18
or due to cardiac motion, respiratory motion, or other body motion.
As such, coupling member 180 may be a continuous member
circumscribing housing 150 to receive a trigger signal from
multiple sides of pacemaker 100. In other embodiments coupling
member 180 may be discontinuous and include multiple segmented
members along the circumference of housing 150. It is contemplated
that numerous configurations for one or more coupling members along
distal end 102, proximal end 104 and/or along the outer
circumference of housing 150 may be conceived.
[0121] FIG. 6 is a functional block diagram of an example
configuration of pacemaker 100. Pacemaker 100 includes a pulse
generator 202, an optional sensing module 204, a control module
206, memory 210, trigger signal receiver 212 and a power source
214. Pulse generator 202 generates electrical stimulation pulses
that are delivered to heart tissue via electrodes 162 and 164.
Control module 206 controls pulse generator 202 to deliver a
stimulation pulse in response to receiving a trigger detect (TD)
signal 216 from receiver 212. In other embodiments, pulse generator
202 may be configured to be enabled to deliver a stimulation pulse
directly by an input signal received from receiver 212. For
example, a switch responsive to a trigger detect signal 216
produced by receiver 212 may enable pulse generator 202 to deliver
a stimulation pulse to a targeted tissue via electrodes 162 and
164.
[0122] Pulse generator 202 includes one or more capacitors and a
charging circuit to charge the capacitor(s) to a pacing pulse
voltage. The pacing capacitor may be charged to the pacing pulse
voltage while control module 206 waits for a trigger detect signal
216 from receiver 212. Upon detecting the trigger signal, the
capacitor is coupled to pacing electrodes 162, 164 to discharge the
capacitor voltage and thereby deliver the pacing pulse.
Alternatively, detection of the trigger signal initiates pacing
capacitor charging and when a predetermined pacing pulse voltage is
reached, the pulse is delivered. Pacing circuitry generally
disclosed in U.S. Pat. No. 8,532,785 (Crutchfield), hereby
incorporated herein by reference in its entirety, may be
implemented in pacemaker 100 for charging a pacing capacitor to a
predetermined pacing pulse amplitude under the control of control
module 206 and delivering a pacing pulse.
[0123] Alternatively, pulse generator 202 may include a switch that
connects power source 214 to pacing electrodes 162 and 164 to
deliver the pacing pulse. The switch is opened by trigger detect
signal 216 or by a control signal from control module 206, and
power source 214 delivers energy to pulse generator 202 for
generating a pacing pulse.
[0124] As described below, control module 206 may determine a
pacing pulse control parameter from the trigger detect signal 216
and use the determined pacing pulse control parameter to control
pulse generator 202 to deliver one or more pacing pulses in
accordance with the determined control parameter. For example, the
pulse width or other aspect of the trigger signal may be determined
by control module 206 and used to set the pulse width (or another
aspect) of the pacing pulse.
[0125] Receiver 212 receives trigger signals through coupling
member 180. Receiver 212 includes one or more receiving
transducers, which may be mounted directly along an inner surface
of coupling member 180, e.g., for receiving sound waves or light.
The trigger signal causes a receiving transducer to produce a
voltage signal that is passed to a comparator included in receiver
212 (or control module 206) for comparison to a trigger signal
detection threshold. If the voltage signal produced by the
receiving transducer is greater than the detection threshold, a
trigger detect signal 216 is passed to control module 206, or
directly to pulse generator 202, to cause pacing pulse
delivery.
[0126] The receiver 212 is configured to detect only the emitting
device-generated trigger signal in some embodiments. For example,
receiver 212 may be "tuned" to detect an acoustical or optical
signal of a particular signal frequency or bandwidth that is
outside a normal physiological range of acoustical or optical
signal sensing. In some examples, receiver 212 is not configured to
sense and process any physiological acoustical signals or optical
signals for determining a physiological event, condition or
state.
[0127] Control module 206 controls pulse generator 202 to deliver a
pacing pulse according to therapy delivery control parameters such
as pulse amplitude, pulse width, pulse number, etc., which may be
stored in memory 210. In some examples, pulse generator 202 is
enabled to deliver a pacing pulse immediately upon receiving a
trigger detect signal 216, either directly from receiver 212 or via
control module 206. Alternatively, the pacing pulse may be
delivered after a predetermined time delay.
[0128] In some examples, pacemaker 100 is solely a therapy delivery
device without sensing capabilities. In other examples, pacemaker
100 may include a sensing module 204 coupled to electrodes 162 and
164 for sensing near-field EGM signals for use in controlling the
delivery of pacing pulses. For example, when pacemaker 100 is
implanted in the LV, R-waves in the LV may be sensed by sensing
module 204. Sensing module 204 generates an R-wave sense event
signal that is provided to control module 206. Control module 206
may start a pacing timing interval upon receiving a trigger detect
signal 216 from receiver 212. If an R-wave sense event signal is
received by control module 206 from sensing module 204 prior to the
pacing timing interval expiring, the scheduled pacing pulse is
inhibited. No pacing pulse is delivered by pulse generator 202. If
the pacing timing interval expires prior to receiving an R-wave
sense event signal from sensing module 204, control module 206
enables pulse generator 202 to deliver the scheduled pacing pulse
at the expiration of the pacing timing interval.
[0129] The pacing timing interval may be, for example, a VV
interval to control delivery of a pacing pulse to the LV (or RV)
relative to an intrinsic R-wave sensed by ICD 14. The pacing timing
interval may be an AV interval to control delivery of a pacing
pulse in a ventricle relative to an intrinsic P-wave sensed by ICD
14. The pacing timing interval may be relative to a pacing pulse
that is delivered in another heart chamber that may also be
delivered by another leadless intracardiac pacemaker that is
triggered to deliver a pacing pulse by a trigger signal from
emitting device 18. For example, ICD 14 may control emitting device
18 to produce a trigger signal. Two different pacemakers implanted
in two different heart chambers may detect the trigger signal. One
pacemaker implanted in one heart chamber may deliver a pacing pulse
first, immediately upon detecting the trigger signal. The other
pacemaker implanted in a different heart chamber may start a pacing
time interval upon detecting the trigger signal. The pacemaker in
the second heart chamber delivers a pacing pulse second, upon
expiration of the pacing timing interval as long as the sensing
module 204 does not produce an intrinsic sensed event signal prior
to the expiration of the pacing timing interval. The second
pacemaker delivers the second pacing pulse at a desired delay after
the first pacing pulse. In this way, ICD 14 may control multiple
intracardiac pacemakers to delivery pacing pulses in timed
coordination with each other using a common trigger signal or using
separate, time-delayed trigger signals.
[0130] Receiver 212 may include multiple receiving transducers for
sensing the trigger signal. The voltage signal produced by multiple
transducers may be summed, for example, for comparison to a trigger
signal detection threshold. In some embodiments, multiple receiving
transducers may be included that are responsive to different
frequency bandwidths. Providing detection of different signal
frequencies may enable different trigger signals to be transmitted
for causing pacemaker 100 to perform different pacing functions
and/or improve trigger signal detection.
[0131] Power source 214 provides power to each of the other modules
and components of pacemaker 100 as required. Control module 206 may
execute power control operations to control when various components
or modules are powered to perform various pacemaker functions.
Power source 214 may include one or more energy storage devices,
such as one or more rechargeable or non-rechargeable batteries.
[0132] Control module 206 may also be configured to perform
diagnostic testing of pacemaker 100, which may include monitoring
the remaining charge of power source 214 and providing a
replacement or end-of-life indicator. Control module 206 is shown
to include a battery monitoring module 218 for monitoring power
source 214. When a remaining battery voltage of power source 214
reaches a threshold level, control module 206 is configured to
adjust a parameter of the pacing pulses delivered by pulse
generator 202 as described below in conjunction with FIG. 17. The
connections between power source 214 and other pacemaker modules
and components are not shown in FIG. 6 for the sake of clarity.
[0133] In some examples, control module 206 includes a trigger
signal (TS) analysis module 220 for analyzing a detected trigger
signal to determine pacing pulse parameter information included in
the trigger signal. The trigger detect signal 216 may be a logic
signal that is set high whenever a receiver transducer voltage
signal exceeds a trigger detect threshold. The TS analysis module
220 may analyze the width, number of pulses, and/or time intervals
between trigger signal pulses to determine a pacing pulse control
parameter from the trigger signal. Control module 206 controls
pulse generator 202 to deliver pacing pulse according to the
determined pacing pulse control parameter. Examples of trigger
signals that include pacing pulse control information are described
below, for example in conjunction with FIGS. 11-15.
[0134] Circuitry represented by the block diagram shown in FIG. 6
may include any discrete and/or integrated electronic circuit
components that implement analog and/or digital circuits capable of
producing the functions attributed to pacemaker 100 herein. The
functions attributed to pacemaker 100 herein may be embodied as one
or more processors, hardware, firmware, software, or any
combination thereof. Control module 206 may include any one or more
of a microprocessor, a controller, a digital signal processor
(DSP), an application specific integrated circuit (ASIC), a
field-programmable gate array (FPGA), state machine, or equivalent
discrete or integrated logic circuitry. Depiction of different
features of pacemaker 100 as discrete modules or components is
intended to highlight different functional aspects and does not
necessarily imply that such modules must be realized by separate
hardware or software components. Rather, functionality associated
with one or more modules may be performed by separate hardware or
software components, or integrated within common or separate
hardware or software components, which may include combinational or
sequential logic circuits, state machines, memory devices, etc.
[0135] Memory 210 may include computer-readable instructions that,
when executed by control module 206, cause control module 206 to
perform various functions attributed throughout this disclosure to
pacemaker 100. The computer-readable instructions may be encoded
within memory 210. Memory 210 may include any non-transitory,
computer-readable storage media including any volatile,
non-volatile, magnetic, optical, or electrical media, such as a
random access memory (RAM), read-only memory (ROM), non-volatile
RAM (NVRAM), electrically-erasable programmable ROM (EEPROM), flash
memory, or other digital media with the sole exception being a
transitory propagating signal. Memory 210 stores intervals,
counters, or other data used by control module 206 to control the
delivery of pacing pulses by pulse generator 202 in response to
detection of a trigger signal received by receiver 212.
[0136] In one embodiment, pacemaker 100 includes only receiver 212,
pulse generator 202 including low voltage charging circuitry and a
pacing capacitor, power source 214 and control module 206, which
may be implemented as a logic circuit for controlling pacing pulse
delivery in response to trigger signal detection. The pacemaker 100
in this example is minimized in size and functionality and does not
include sensing module 204 for receiving physiological signals and
does not include an RF transceiver or amplifier included in
standard bi-directional telemetry circuitry. FIG. 7 is a block
diagram of one example of receiver 212 of pacemaker 100.
[0137] A receiving transducer 282, which may include one or more of
the transducers listed above or an RF antenna, produces a voltage
output signal 283 when subjected to a trigger signal emitted by
emitting device 18. Receiving transducer 282 may have a relatively
narrow or wide bandwidth characterized by a center frequency or
wavelength that approximately matches the center frequency or
wavelength of the transmitting transducer included in the trigger
signal emitting device 18.
[0138] A rectifier and filter circuit 284 receives the voltage
output signal 283 and produces a rectified and filtered signal 285
correlated to the trigger signal converted to an electrical signal
by transducer 282. The rectified and filtered signal 285 is
provided as input to comparator 286. Comparator 286 receives a
detection threshold signal Vthresh 287, e.g., from power source
214, that is compared to rectified and filtered signal 285. When
signal 285 exceeds Vthresh 287, a trigger detect signal 216 is
produced and passed to the pacemaker control module 206 for
triggering pacing pulse delivery. In some examples, trigger detect
signal 216 is solely a trigger signal that causes pacing pulse
delivery.
[0139] In other examples, trigger detect signal 216 includes pacing
pulse control parameter information, in which case control module
206 analyzes the trigger detect signal 216 to determine a pacing
control parameter. The trigger detect signal 216 output from
receiver 212 may be a logic signal that is high as long as the
filtered rectified signal 285 is greater than Vthresh 287. The
characteristics of pulses included in trigger detect signal 216,
such as pulse number, pulse width, interpulse interval, etc., may
be interpreted by TS analysis module 220 of pacemaker 100 for
setting pacing pulse parameters and controlling pacing pulse
delivery by pulse generator 202.
[0140] FIG. 8 is a plot of a rectified and filtered voltage signal
285 provided to comparator 286 of the receiver 212 shown in FIG. 7.
As long as the rectified filtered signal 285 is greater than
Vthresh 287, the comparator 286 passes a trigger detect signal 216
to the pacemaker control module 206. The leading edge 292 of
trigger detect signal 216 starts upon the rising crossing 293 of
Vthresh 287 by signal 285. The trailing edge 294 of trigger detect
signal 216 occurs upon the falling crossing 295 of Vthresh 287 by
signal 285. The trigger detect signal 216 has a width (time
duration) 296 equal to the time that the rectified filtered voltage
signal 285 is greater than Vthresh 287. Control module 206 may
determine this signal width 296 and set a pacing pulse control
parameter, such as pacing pulse width, in response to the signal
width 296 in some examples. In other examples, as described below,
control module 206 may control the onset and/or offset of a pacing
pulse upon receiving trigger detect signal 216 without determining
the signal width 296. In still other examples, the control module
may count a number of trigger detect signals 216 for use in
selecting a pacing pulse control parameter and controlling pacing
pulse delivery.
[0141] In another embodiment, a second threshold 287' in addition
to Vthresh 287 may be added to determine a time interval 297
between a first threshold crossing 293 and a second threshold
crossing 293'. The second threshold crossing 293' may be detected
by implementing a second comparator in comparator 286 of receiver
212 to produce a second trigger detect output signal 216'. The time
interval 297 between two different threshold crossings 293 and 293'
is determined by TS analysis module 220 of pacemaker 100 to
determine a rising and/or falling slope 298 of trigger signal 285.
The determined slope 298 may be used to validate a detected trigger
signal 285, distinguish between mutually exclusive trigger signals
intended for different therapy delivery devices when multiple
therapy delivery devices are implanted, and/or indicated a pacing
pulse parameter setting encoded in the trigger signal 285.
[0142] FIG. 9 is a flow chart 250 of a method for controlling
therapeutic stimulation pulses delivered by an implantable medical
device system, such as system 2, 10, 10', 10'' or 11 shown in FIGS.
1 through 3C. Flow chart 250 and other flow charts presented herein
are intended to illustrate the functional operation of the system,
and should not be construed as reflective of a specific form of
software or hardware necessary to practice the methods described.
It is believed that the particular form of software, hardware
and/or firmware will be determined primarily by the particular
system architecture employed in the sensing device 4 and the
therapy delivery device 6 and by the particular sensing and therapy
delivery methodologies employed by the system 2. Providing
software, hardware, and/or firmware to accomplish the described
functionality in the context of any modern pacemaker system, given
the disclosure herein, is within the abilities of one of skill in
the art. Methods described in conjunction with flow charts
presented herein may be implemented in a computer-readable medium
that includes instructions for causing a programmable processor to
carry out the methods described. The instructions may be
implemented as one or more software modules, which may be executed
by themselves or in combination with other software.
[0143] At block 252, and with reference to system 2 of FIG. 1, a
sensing device 4, senses physiological events that are used to
coordinate therapeutic stimulation pulses. The physiological events
may be R-waves or P-waves sensed from an ECG signal. At block 254,
the sensing device 4 controls emitting device 5 to emit trigger
signals 7 by applying a drive signal to an emitting device
transducer. The trigger signals are detected by therapy delivery
device 6 at block 256, which may be a pacemaker such as pacemaker
100. The therapy delivery device 6 delivers therapeutic stimulation
pulses in response to detecting the trigger signal 7. The trigger
signal 7 is emitted at time intervals that cause the therapeutic
stimulation pulses to be delivered at block 258 within a range of a
target time interval relative to the sensed physiological events.
For example, a ventricular pacing pulse may be delivered by therapy
delivery device 6 within a range of a target AV delay following a
P-wave sensed by sensing device 4.
[0144] One trigger signal 7 may be delivered following each sensed
event to coordinate a therapeutic stimulation pulse with each
sensed event, e.g., one ventricular pacing pulse for each P-wave
sensed event. The trigger signal 7 is emitted at a time interval
relative to the sensed physiological event to cause the therapy
delivery device 6 to deliver the therapeutic stimulation pulse
within a range of a targeted time interval from the sensed
physiological event. In other words, the trigger signals emitted by
emitting device 5 and therapeutic stimulation pulses have a 1:1
correspondence.
[0145] The trigger signals emitted over a time interval including
two or more sensed physiological events may have a total combined
time duration that is equal to the total combined time duration of
the associated triggered therapeutic stimulation pulses. In other
words, for each trigger signal, one pacing pulse may be delivered
and the trigger signal and the pacing pulse may have the same
signal width. However, since trigger signal emission may require
significant battery consumption, in other examples the total
combined time duration of the trigger signals is less than the
total combined time duration of the therapeutic pulses invoked by
the trigger signals. The trigger signals may be emitted at a rate
that is less than the rate of the therapeutic stimulation pulses.
The trigger signals may be emitted at a signal width that is less
than the pulse width of the therapeutic stimulation pulses. In some
examples, the trigger signals are emitted at a rate and signal
width that is less than the rate and pulse width of the therapeutic
stimulation pulses. In other words, in some examples the trigger
signals may have less than a 1:1 correspondence with the
therapeutic stimulation pulses in duration and/or number (rate).
For example, one trigger signal may trigger therapy delivery device
6 to deliver a series of therapeutic stimulation pulses so that a
trigger signal is not delivered every time a stimulation pulse is
delivered. To illustrate, one trigger signal may be emitted by
emitting device 5 in response to a P-wave sensed by sensing device
4, causing therapy delivery device 6 to deliver a series of 2, 4,
6, 8 or other number of pacing pulses at a fixed rate in response
to the one trigger signal.
[0146] In another example, the trigger signal may have a pulse
duration that is less than a stimulation pulse duration (width).
Therapeutic stimulation pulses may be delivered by therapy delivery
device 6 in a 1:1 correspondence with detected trigger signals 7,
but trigger signals 7 may be emitted with a shorter signal width
than the pulse width of the stimulation pulses. Battery energy is
saved by using techniques that reduce the total combined time of
the trigger signals compared to the total combined time of the
therapeutic stimulation pulses.
[0147] FIG. 10 is a flow chart 270 of a method for controlling
triggered therapeutic stimulation pulses according to another
example. With reference to system 2 of FIG. 1, a physiological
event is sensed by sensing device 4 at block 272. A transducer of
emitting device 5 is controlled at block 274 by control signal 3
from sensing device 4 to emit a trigger signal 7 that includes
stimulation pulse control parameter information. The therapy
delivery device 6 may not include a transceiver for standard RF
communication capability that enables bi-directional communication
with amplification of a received signal to enable programming of
therapy delivery control parameters using an external programmer.
As such, the trigger signal 7 may be used to transfer therapy
control parameter information to the therapy delivery device (in
addition to triggering stimulation pulse timing). Therapy control
parameter information may include, without limitation, stimulation
pulse amplitude, stimulation pulse width, stimulation pulse train
frequency, number of stimulation pulses in a pulse train, or other
stimulation pulse characteristics.
[0148] At block 276, the therapy delivery device 6 detects the
trigger signal 7 and determines the control parameter from the
trigger signal 7. The control parameter information is included in
the trigger signal 7 by coding the trigger signal pulse width,
signal frequency, signal amplitude, pulse number, pulse interval,
or other aspect of the trigger signal 7 that is detectable by the
therapy delivery device 7, e.g., as determined by TS analysis
module 220 shown in FIG. 6.
[0149] In response to the trigger signal, the therapy delivery
device 6 delivers one or more therapeutic stimulation pulses to a
targeted tissue at a targeted time interval according to the
control parameter determined from the trigger signal 7. The
stimulation pulse is delivered immediately or after a predetermined
time delay after detecting trigger signal 7 such that the
stimulation pulse is delivered within a targeted time interval
range from the physiological event sensed by sensing device 4. The
stimulation pulse itself is defined at least in part by the
determined control parameter. For example, the pulse width or pulse
amplitude may be set based on the determined control parameter
coded in the trigger signal 7. In this way, the trigger signal 7
controls both the timing and a feature of the pulse delivered by
therapy delivery device 6.
[0150] FIG. 11 is a timing diagram 300 of a trigger signal 306 and
resulting pacing pulse 314 according to one example. A sensing
device 4 (or ICD 14), monitors an ECG signal 301 for sensing a
cardiac event 302, e.g., a P-wave or an R-wave. When the ECG signal
301 crosses a sensing threshold 304, a cardiac event 302 is sensed.
Sensed cardiac event 302 is a P-wave in one illustrative example.
The sensing device 4 starts a pacing timing interval 312, e.g., an
atrioventricular (AV) interval, upon sensing event 302. The pacing
timing interval 312 is set based on a desired time interval between
the sensed cardiac event 302 and a pacing pulse 314 less any system
delay between initiating a trigger signal 306, producing a trigger
detect signal 310 and delivering the pacing pulse 314.
[0151] At expiration of the pacing timing interval 312, the
emitting device 18 is enabled to emit a trigger signal 306 at a
predetermined frequency or wavelength for a time duration that
defines the trigger signal pulse width 308. A trigger detect signal
310 is produced by a receiver of the therapy delivery device 6,
e.g., the pacemaker receiver 212 shown in FIG. 6, for the entire
trigger signal width 308 over which the rectified trigger signal
306 exceeds a trigger detection threshold (not illustrated in FIG.
11).
[0152] The therapy delivery device 4 starts the therapeutic
stimulation pulse 314, which is a pacing pulse in this example, in
response to the trigger detect signal 310. For example, a pacing
capacitor of pacemaker 100 may be discharged through the pace
electrodes 162 and 164 until the rectified trigger signal 306 falls
below the trigger signal detection threshold. The pacing pulse 314
may be terminated with the trailing edge of the trigger detect
signal 310, i.e., when the rectified trigger signal 306 falls below
the trigger detection threshold, by disconnecting the pacing
capacitor from the pacing electrodes 162 and 164. The pacing pulse
width 316 is equal to the time interval that the trigger detect
signal 310 is high, which matches the width 308 of the emitted
trigger signal 306. In other examples, the therapy delivery device
6 may be configured to start the leading edge of pacing pulse 314
after a time delay following the onset of trigger detect signal 310
and have a pulse width equal to the width 308 of the trigger signal
306. In the example shown in FIG. 11, there is a 1:1 correspondence
between the width 308 of trigger signal 306 and pacing pulse width
316.
[0153] The pacing pulse amplitude 318 may be a fixed parameter in
some examples. The pacing pulse amplitude may be set at a fixed
voltage, for example 1.5 V. Alternatively, the pacing pulse
amplitude 318 may set to a fixed fraction of the therapy delivery
device battery voltage, for example one half the battery voltage of
power source 214 of FIG. 6. The pacing pulse width 316 is
controlled by the trigger signal width 308 to deliver a pacing
pulse energy that successfully captures the cardiac tissue (or
other targeted tissue).
[0154] FIG. 12 is a timing diagram 400 of an alternative method for
controlling a pacing pulse parameter using a trigger signal. With
reference to system 10 of FIG. 2A, the ECG signal 401 is monitored
by ICD 14 to detect a cardiac event 402. In one example, sensed
event 402 is a P-wave sensed by ICD 14 based on a sensing threshold
404. One method for sensing a P-wave by ICD 14 is generally
disclosed in commonly-assigned U.S. patent application Ser. No.
14/524,090, filed on Oct. 27, 2014 (Greenhut, et al.), incorporated
herein by reference in its entirety. A pacing timing interval 412,
which is an AV interval in this example, is started by control
module 80 of ICD 14. Upon expiration of the AV interval 412, timing
module 92 sends a control signal 95 to the emitting device 18.
Emitting device 18 emits a trigger signal 406 at a predefined
trigger signal frequency or wavelength for a relatively short
signal width 408. Receiver 212 detects the trigger signal 406 and
produces a trigger detect signal 410. The trigger detect signal 410
is passed to pacemaker control module 206, as long as the
rectified, trigger signal 406 remains above a trigger detection
threshold (not illustrated).
[0155] The pacemaker trigger signal analysis module 220 determines
the trigger signal width 408 based on the duration of the trigger
detect signal 410 and controls the pulse generator 202 to deliver
pacing pulse 414 with a pulse width 416 that is a multiple of the
trigger signal width 408. Trigger signal 406 may be emitted at a
rate having a 1:1 ratio with the number of pacing pulses 414 that
are delivered by pacemaker 100, but the time that each trigger
signal 406 is transmitted, i.e., the signal width 408, is shorter
than the pacing pulse width 416 to conserve battery energy supplied
to emitting device 18 from ICD 14 and/or conserve a dedicated
emitting device battery. Alternatively, the rate of trigger signal
406 may be less than a 1:1 rate with pacing pulses 414 such that
for each trigger signal 406, more than one pacing pulse 414 is
delivered at a fixed rate.
[0156] The pacing pulse amplitude 418 may be fixed as described
above. The trigger signal 406 can be controlled by the control
signal 3 to be emitted for different, incremental signal widths
408. The width of the detected trigger signal 410 is used by
pacemaker 100 to control the pacing pulse width 416 as a fixed
multiple of the trigger signal width 408. In this way, the trigger
signal width 408 is not required to be equal to the pacing pulse
width 416 but the trigger signal 408 contains pacing pulse control
parameter information.
[0157] To illustrate, a multiple N may be stored as a fixed value,
e.g. 8, in pacemaker memory 210. The emitting device 18 is
controlled by control signal 95 to emit trigger signal 406 for 0.05
ms, e.g. 50 cycles of a 1 MHz signal frequency. The trigger detect
signal 410 is produced by the pacemaker receiver 212 having a width
substantially equal to the time that the trigger signal 406 is
greater than the trigger detection threshold, e.g., Vthresh 287 as
shown in FIG. 10. The pacemaker control module 206 measures the
width of the trigger detect signal 410, e.g., using a digital timer
or counter included in TS analysis module 220 of control module
206. The control module 206 includes a multiplier for multiplying
the trigger detect signal width by the stored multiple N to set the
pacing pulse width 416. Control module 206 enables pulse generator
202 to deliver pacing pulse 414 at a fixed pulse amplitude 418 and
the determined pulse width 416 of 0.4 ms in this example (0.05 ms
multiplied by 8).
[0158] FIG. 13 is a timing diagram 500 illustrating another example
method for controlling pacing pulse delivery using trigger signals.
A cardiac event 502 is sensed by ICD 14 from the ECG signal 501
based on a sensing threshold 504. ICD 14 starts the pacing timing
interval 512 upon sensing event 502, and controls emitting device
18 to transmit a first trigger signal pulse 506a upon expiration of
the pacing timing interval 512.
[0159] In this example, the trigger signal includes a pair of
pulses 506a and 506b, collectively 506. ICD control module 80 sends
a first control signal to emitting device 18 to cause emission of
the first trigger signal pulse 506a, waits a timed interpulse
interval 520, and then sends a second control signal to emitting
device 18 to cause emission of the second trigger signal pulse
506b. The total trigger signal width 508 of the trigger signal 506
is defined by the first pulse 506a, the interpulse interval 520,
and the second pulse 506b. The duration of each individual pulse
506a and 506b may be minimized to reduce battery consumption
required for producing trigger signal pulses 506a and 506b.
[0160] The pacemaker receiver 212 produces a pair of trigger detect
signals 510a and 510b when the respective trigger signal pulses
506a and 506b are greater than the trigger detection threshold
(e.g., Vthresh 287 of FIG. 8). Receiver 212 detects each trigger
signal pulse 506a and 506b, spaced apart by inter-pulse interval
520. In response to trigger detect signal 510a, the pulse generator
202 starts pacing pulse 514 by coupling the pacing capacitor to the
pace electrodes 162, 164. In some cases, the pacing capacitor of
pulse generator 202 is pre-charged. In other cases, pacing
capacitor charging is started upon trigger detect signal 510a such
that a short system delay between trigger detect signal 510a and
pacing pulse 514 may exist.
[0161] In response to the second trigger detect signal 510b, the
pulse generator 202 uncouples the pacing capacitor from the pace
electrodes 162 and 164 to terminate the pacing pulse 514. The
pacemaker control module 206 controls pulse generator 202 to
deliver pacing pulse 514 with a leading edge 522 coincident with
trigger detect pulse 510a and a trailing edge 524 coincident with
trigger detect pulse 510b.
[0162] In this way, pacing pulse 514 is delivered with a pacing
pulse width 516 substantially equal to the trigger signal width 508
without requiring trigger signal emission for the entire duration
of signal width 508. The pacing pulse amplitude 518 may be fixed as
described previously. The pacing pulse energy delivered to capture
the heart is controlled by varying the trigger signal interpulse
interval 520, and thereby varying the timing of the second trigger
detect signal 510b and coincident trailing edge 524 of pacing pulse
514.
[0163] In another example, pacemaker 100 may be configured to
measure the interpulse interval 520 by determining the time
interval between trigger detect signals 510a and 510b and
multiplying the interpulse interval 520 by a fixed value to obtain
pacing pulse width 516. The trigger signal pulses 506a and 506b may
be delivered at an interpulse interval 520 that is a fraction of
the total pacing pulse width 516.
[0164] The pulses 506a and 506b may be identical pulses. In other
examples, pulse 506b may have at least one pulse characteristic
different than pulse 506a to be distinguishable as the terminating
pulse 506b and the starting pulse 506a. For example, starting pulse
506a may have a pulse width that is greater than or less than pulse
506b, a frequency that is greater than or less than 506b, or an
amplitude that is greater than or less than pulse 506b. In this
way, if a terminating pulse 506b is detected without a preceding
starting pulse 506a, the pacemaker 100 will not initiate a pacing
pulse. Likewise, if a starting pulse 506a is detected but a
terminating pulse 506b is not detected within some maximum time
interval, the pacing pulse 514 may be automatically truncated as a
predefined maximum pulse width.
[0165] FIG. 14 is a timing diagram 600 of another method for
controlling pacing pulses using a trigger signal. The cardiac event
602 is sensed by the ICD 14 when the ECG signal 601 crosses a
sensing threshold 604. The pacing timing interval 612 is started by
ICD control module 80 upon sensing event 602. Upon expiration of
the pacing timing interval 612, ICD 14 sends a control signal 95 to
emitting device 18 that causes emitting device 18 to emit a trigger
signal 606 having a variable number of pulses. The number of pulses
N is set by control signal 95.
[0166] The pacemaker receiver 212 detects the trigger signal pulses
and produces a trigger detect signal 610 having N pulses equal to
the number of pulses in the trigger signal 606 that exceed the
trigger detection threshold. The TS analysis module 220 of
pacemaker control module 206 counts the number of pulses in the
trigger detect signal 610 and multiplies that number by a fixed
time interval, e.g. 0.10 ms, stored in memory 208 to determine the
pacing pulse width 616.
[0167] Control module 206 controls pulse generator 202 to deliver
pacing pulse 614 having a fixed pulse amplitude 618 and a variable
pulse width 616 set equal to the number of pulses of trigger detect
signal 610 multiplied by the time interval stored in memory 208.
ICD 14 thereby controls pacing pulse width 616 by controlling how
many pulses are emitted by emitting device 18 in each trigger
signal 606. The pacing pulse width 616 may be incremented or
decremented by the time interval stored in pacemaker memory 208 by
increasing or decreasing the number of pulses in the trigger signal
606. In the example, shown four pulses in trigger signal 606 are
detected as four pulses in trigger detect signal 608. The pacemaker
control module 206 multiples four by a stored time interval, e.g.
0.1 ms, to obtain a pacing pulse width 616 of 0.4 ms.
[0168] The pulses in trigger signal 606 are delivered at the
trigger signal frequency, (for example 1 MHz) or wavelength (for
example 1100 nm) for an individual pulse width that can be
minimized to reduce battery consumption. The individual pulse
width, however, must be detectable by the pacemaker receiver 212.
The interpulse interval 620 is long enough that the individual
pulses of trigger signal 606 can be detected by pacemaker receiver
212. The total width 608 of trigger signal 606 defined by the N
individual pulses and the interpulse interval 620 is not greater
than pacing pulse width 616 and will typically be shorter than the
pacing pulse width 616 so that the pacing pulse 614 can be
terminated at the correct width 616.
[0169] In the example of FIG. 14, the interpulse interval 620 is
equal between all pulses of trigger signal 606. The pacemaker
control module 206 may wait for at least two interpulse intervals
620 before determining the pacing pulse width so that if one pulse
is missed (not detected) the next pulse, occurring at twice the
expected trigger signal pulse interval 620 may be counted twice to
account for the missed pulse.
[0170] In the examples of FIGS. 13 and 14 that require the
pacemaker 100 to determine the pacing pulse width from the trigger
signal width or the trigger signal pulse number, the onset of the
pacing pulse 514, 614 may be set to occur after a delay interval
from the onset of the trigger detect signal 506, 606 to allow
processing time required to determine the final pacing pulse width.
It is understood that an inherent signal processing delay between
the time that the ICD 14 sends the control signal 95 to the
emitting device 18 and the earliest time that the pacing pulse 514
or 614 can be initiated or terminated may exist. The various timing
intervals, such as the pacing timing intervals 512 and 612 and the
interpulse intervals 520 and 620 and any pacemaker applied delay
time before delivering pacing pulse 514 or 614 will be selected to
account for this signal processing delay required to determine a
pacing pulse parameter from the trigger detect signal 510 or 610
and still provide accurate timing of pacing pulses 514 and 614
relative to the sensed cardiac event 502 and 602, respectively.
[0171] FIG. 15 is a timing diagram 650 of a trigger signal 651 that
includes a train of four pulses 652, 654, 656 and 658. Each pulse
652, 654, 656 and 658 is delivered at a selected trigger signal
frequency or wavelength for an individual pulse duration that is at
least a minimum pulse duration detectable by the pacemaker receiver
212. In this example, the interpulse intervals 670, 672 and 674 are
different from each other in contrast to the equal interpulse
intervals 620 shown in the example of FIG. 14. Predetermined
interpulse intervals 670, 672, and 674 that are different from each
other can facilitate correct counting of the number of trigger
signal pulses 652, 654, 656, and 658 by the pacemaker 100. The
interpulse intervals 670, 672 and 674 may decrease by a
predetermined decrement between consecutive pulses. Alternatively
interpulse intervals may increase or vary bi-directionally between
consecutive pulses.
[0172] The first pulse 652 and second pulse 654 of trigger signal
651 are separated by an interpulse interval 670, which may
correspond to a minimum pacing pulse width or a fraction of the
minimum pacing pulse width. Upon detecting the first pulse 652, the
pacemaker 100 increments a pulse counter included in trigger signal
analysis module 220 and waits for a second pulse 654 at the
interval 670. Upon detecting the second pulse 654, the pulse
counter is incremented by one to a count of two. The next pulse 656
is expected at the decremented interval 672. If pulse 656 is not
detected by pacemaker 100, as indicated by dashed line, the
pacemaker 100 may wait for at least one next interpulse interval
674 to determine if any additional trigger signal pulses are
detected. If pulse 658 is detected by pacemaker 100 at a combined
interval equal to interval 672 plus interval 674, the pacemaker 100
determines that pulse 656 was missed. Pacemaker 100 will increment
the pulse counter by two (to a count of four) based on the detected
pulse 674 and the determination that pulse 656 was missed.
Pacemaker 100 then waits for the next decremented interval 676.
[0173] In this example, the trigger signal 651 is four pulses (670
through 674) long. The short dashed lines 660 and 662 represent
additional trigger signal pulses that may be present if the trigger
signal is more than four pulses long. All six pulses 652 through
662 may represent a maximum number of trigger signal pulses and
correspond to a maximum pacing pulse width. If no pulse is detected
at interval 676, pacemaker 100 may wait at least one more interval
678 to determine if pulse 660 was missed. If two expected
interpulse intervals 676 and 678 expire without detecting any
additional pulses, the pacemaker control module 206 counts a total
of four pulses, even though pulse 656 was not detected, based on
three detected pulses 652, 654 and 658 and the total time of
intervals 672 and 674 between detected pulses 654 and 658 that
indicates pulse 656 was missed.
[0174] The pacemaker control module 206 controls pulse generator
202 to deliver pacing pulse 682, which may have a fixed amplitude
690, with a pulse width 688 determined as a multiple of the number
of counted pulses in trigger signal 651. The pacing pulse 682 is
terminated at trailing edge 686 based on the determined pulse width
688.
[0175] In this example, the leading edge 684 of pulse 682 is
started after a delay interval 680 to allow the pacemaker receiver
212 time to receive the first three pulses 652, 654 and 656. If
only one pulse 652 is detected after waiting for the second and
third pulses 654 and 656, the pacing pulse width can be set to a
minimum pulse width (one detected pulse times a fixed time interval
stored in memory 210). Thus the delay interval 680 allows pacemaker
100 time to detect at least the first three trigger signal pulses
652, 654 and 656 before determining and setting the pacing pulse
width 688.
[0176] In other examples, the interpulse intervals 670, 672, 674,
676, and 678 may be short enough that the leading edge 684 of
pacing pulse 682 may be started upon detection of the first trigger
signal pulse 652, and pacemaker 100 determines the pacing pulse
width 688 during pacing pulse 682 by counting the total number of
trigger signal pulses and multiplying that number by a fixed
interval stored in memory 210. In still other examples, the delay
interval 680 may be set to a value that is greater than a maximum
trigger signal width 664 to enable pacemaker 100 to detect all
pulses up to a maximum number of pulses, six in this example, and
determine the pacing pulse width 688 prior to starting pacing pulse
682.
[0177] Additionally, the pacemaker signal receiver 212 may apply
noise rejection intervals (NRIs) 666 during the interpulse
intervals 670 through 678. NRIs 666 are time intervals during which
a detected signal pulse is rejected as noise. The preceding signal
pulse detected outside the NRI 666 may also be rejected as an
invalid pulse. For example, if signal pulse 652 is detected, the
pacemaker signal receiver may start a NRI 666. If another signal
pulse is detected during NRI 666, it is rejected as noise and the
signal pulse 652 that caused the NRI 666 to be started is also
rejected as noise and not part of a valid trigger signal. The next
time a signal pulse is detected, a new NRI 666 is started.
[0178] If no signal pulse is detected during the NRI 666, a
detection interval 668 is started upon the expiration of the NRI
666. The detection interval 668 is a short time interval that
starts at or just prior to the end of the interpulse interval 670,
which may be stored in pacemaker memory 210. A signal pulse 654
detected during the detection interval 668, along with the prior
detected signal pulse 652 without any intervening pulses detected
during the NRI 666 is evidence of a valid trigger signal.
Subsequent NRIs 666 are started following each detected trigger
signal pulse (or each detection interval 668 in case of a missed
pulse, e.g., pulse 656). Any signal pulse detected during any of
the NRIs 666 will cause any previously detected pulses during
detection intervals 668 to be determined as noise and not counted
as trigger signal pulses and will not lead to the detection of a
valid trigger signal.
[0179] As shown in FIG. 15, the NRIs may decrease in duration as
the interpulse intervals 670 through 678 decrease in duration. Each
NRI 666 may be a portion or percentage of a known interpulse
interval. Each detection interval 668 may be a multiple of the
width of each trigger signal pulse 652 through 662. A trigger
signal pulse detected during any of the NRIs 666 may cause
rejection of all detected pulses, including those detected during a
detection interval 668. Pulses detected during the detection
intervals 668, when no pulses are detected during any of the NRIs
666, are counted and lead to the detection of a valid trigger
signal by pacemaker 100.
[0180] The pacemaker 100 may count the number of trigger signal
pulses of a valid trigger signal 651 for multiplying by a stored
factor to determine the pacing pulse width 688 as described above.
Alternatively, the pacemaker 100 may count the number of trigger
signal pulses of a valid trigger signal 651 to cause an adjustment
of a previously delivered pacing pulse parameter, such as pulse
width. For example, if the maximum possible number of pulses in a
valid trigger signal 651 is four, detection of a trigger signal
having exactly two pulses may cause the pacemaker 100 to deliver a
pacing pulse 682 at the same pulse parameter as a previous pulse,
e.g., the same pulse width 688. If exactly three trigger signal
pulses are counted, the pacemaker 100 may increase the pacing pulse
parameter by a stored increment, e.g., increase pacing pulse width
by 100 .mu.s. If all four possible trigger signal pulses are
counted in a valid trigger signal 651, the pacemaker 100 may
decrease a pacing pulse parameter by a stored decrement, e.g.,
decrease pacing pulse width 682 by 100 .mu.s.
[0181] FIG. 16 is a flow chart 700 of a method for setting a pacing
pulse width by performing a pacing threshold search in a triggered
pacemaker system, such as system 2, 10, 10', 10'' or 11, according
to one example. Decisions and blocks shown in dashed box 701
represent operations performed by the sensing device that is
producing a control signal passed to the emitting device. In the
examples described herein, box 701 represents functions performed
by ICD 14 and emitting device 18. Decisions and steps shown in
dotted box 703 represent operations performed by the therapy
delivery device that is detecting the trigger signal and delivering
therapeutic stimulation pulses. In the illustrative example, box
703 represents functions performed by pacemaker 100.
[0182] In one example, the threshold search is performed according
to flow chart 700 for determining the capture threshold of the LV.
In this example, the LV is paced by pacemaker 100 at a target AV
interval following a P-wave for delivering CRT. It is recognized,
however, that the methods of the threshold search can be applied to
other pacing or electrical stimulation therapy applications. The
particular cardiac events sensed by the sensing device for starting
a pacing timing interval may be atrial or ventricular, paced or
sensed events, for example. The pacing timing interval started upon
a cardiac event may correspond to an AV interval, a W interval or a
VA interval. The targeted tissue receiving the pacing pulse or
electrical stimulation therapy may be any cardiac or neural tissue.
Further, it is recognized that the threshold search and method for
controlling the pacing pulse width as generally described in
conjunction with FIG. 16 may be adapted to other non-cardiac
therapies, such as stimulation of the phrenic nerve or other
therapies which require capture of a targeted muscle or nerve.
[0183] At decision block 702, the ICD 14 determines if it is time
to perform a threshold search. A threshold search may be performed
at a scheduled time of day, in response to a user command, or in
response to a change in a physiological signal that the ICD 14 is
monitoring that may indicate that loss of capture has occurred. If
it is time for a threshold search, the ICD 14 enters a threshold
search mode of operation by advancing to block 710, where an
initial test pulse width (PW) is set. In the examples described
herein, pacing pulse amplitude is fixed and the PW is adjusted to
achieve capture of the targeted tissue, e.g., the LV myocardium.
The initial PW may be set to a maximum PW or a PW previously known
to cause capture. The threshold search is performed to determine a
minimum PW that achieves capture of the LV when the pacing pulse
amplitude is set to a fixed value.
[0184] At block 712, the ICD 14 senses a P-wave and starts a test
AV interval at block 714. The test AV interval may be a shortened
AV interval compared to an AV interval used during normal LV
pacing. A shortened AV interval may be used during the threshold
search to promote pacing pulse delivery earlier than an
intrinsically conducted depolarization to the LV to avoid false
capture detection due to an intrinsic depolarization arriving ahead
of, or simultaneously with, a pacing-induced depolarization. To
illustrate, the AV interval may be set to 80 ms for delivering LV
pacing during CRT. The AV interval may be shortened to 50 ms during
a threshold search.
[0185] When the test AV interval expires, the ICD 14 sends a
control signal 95 to the emitting device 18 at block 716 to cause
the emitting device 18 to send a trigger signal that includes PW
information. The trigger signal may have a signal width equal to
the PW set at block 710 as described in conjunction with FIG. 11,
include a starting and terminating pulse that indicate the time of
the leading and trailing edges of the pacing pulse as described in
conjunction with FIG. 13, or have a signal width or number of
pulses that are used by the pacemaker 100 to determine the initial
pacing pulse width as described in conjunction with FIGS. 12, 14
and 15.
[0186] Now referring to pacemaker operations 701, the pacemaker
receiver 212 detects the trigger signal at block 752. The pacemaker
100 may charge the pacing capacitor at block 750 while waiting to
receive the trigger signal. Upon receiving the trigger signal, a
delay timer is started at block 754. A delay time may be set by the
pacemaker between a trigger detect signal produced by the pacemaker
receiver 212 and delivery of the triggered pacing pulse, e.g.,
delay time 680 shown in FIG. 15. The delay timer is optional or may
be set to zero during the threshold search.
[0187] The trigger detect signal may be analyzed by TS analysis
module 220 of control module 206 to determine if the trigger signal
is a threshold search trigger signal or a therapy trigger signal.
For example, at block 756, the pacemaker 100 determines if the
trigger signal is shorter than a threshold signal width used to
discriminate between a therapy pace trigger signal and a threshold
search trigger signal. A therapy pace trigger signal may be set a
minimum duration that is reliably detectable by the pacemaker. The
detected trigger signal may be determined to be a "short" trigger
signal at block 756 by determining the width of the trigger detect
signal produced by the pacemaker receiver 212 and comparing the
trigger detect signal width to a threshold width. If the detected
trigger signal is less than the threshold width, the trigger signal
is a therapy trigger signal not a threshold search trigger signal.
If the trigger detect signal width is greater than the threshold
width, the trigger signal is a threshold search trigger signal and
includes information used by the pacemaker 100 to set the pacing PW
to a test PW for determining capture.
[0188] In response to detecting a threshold search trigger signal
at block 756, the pacemaker 100 determines the pacing PW from the
detected trigger signal at block 758. As discussed above, the
threshold search trigger signal may be controlled to include PW
information according to any of the methods described in
conjunction with FIGS. 11 through 15.
[0189] A previously-used pacing PW stored by the pacemaker 100 is
updated at block 760 as the PW determined at block 758 from the
threshold search trigger signal. At block 762, upon expiration of
the delay timer if set, a pacing pulse is started by coupling a
stored charge to pacing electrodes 162 and 164, and a PW timer is
started. The PW timer is set to the PW stored at block 760. When
the PW timer expires, the pacing pulse is terminated at block 764.
The pacing capacitor is recharged at block 750 while the pacemaker
100 waits for the next trigger signal.
[0190] Meanwhile, referring again to ICD operation 701, the ICD 14
monitors the ECG signal at block 720 to determine if capture of the
LV occurred after sending the trigger signal at block 716. Capture
may be detected by the ICD 14 based on sensing an R-wave by sensing
module 86 at the test AV interval or based on detection of a paced
R-wave morphology different than an intrinsic R-wave morphology by
cardiac signal analyzer 90 or a combination thereof.
[0191] If capture is detected at block 720, the pacing PW is
decreased at block 722. The process returns to block 712, to sense
a P-wave and start another test AV interval at block 714. When the
test AV interval expires, the emitting device 18 is controlled to
send a trigger signal for setting a new, decreased pacing PW at
block 716. The pacemaker 100 receives the trigger signal and
detects it as a threshold search trigger signal at block 756 as
described above. The pacemaker 100 determines the new, decreased PW
by analysis of the trigger signal at block 758 (e.g., analysis of
the trigger signal width or pulse number as described above),
updates the previously stored PW at block 760, and delivers a
pacing pulse at the new PW at blocks 762 and 764.
[0192] This process continues until the ICD 14 does not detect
capture at block 720. Failure to detect capture indicates that the
currently stored PW in the pacemaker 100 is less than the capture
threshold. The PW needs to be reset to a supra-threshold interval.
At block 724, the PW is set to the previous PW that did result in
capture plus a nominal safety interval, e.g. 0.10 ms. The previous
PW that did result in capture is determined as the capture
threshold PW. The pacing PW for therapy delivery is set to the
capture threshold PW plus a safety margin interval to reduce the
likelihood of loss of capture due to small fluctuations in the
capture threshold.
[0193] At block 726, a test complete flag is set indicating that
the threshold search is complete. At the next sensed P-wave (block
712), the test AV interval is started again (block 714) and the
trigger signal is sent at block 716 for setting the PW at the
threshold PW plus the safety margin. With the test complete flag
set, as determined at block 718, the ICD 14 now transitions into a
therapy delivery mode of operation by advancing to block 704 to
wait for the next P-wave.
[0194] Meanwhile the pacemaker 100 receives the final threshold
search trigger signal that is setting the PW to the threshold PW
plus the safety margin. At block 752, the trigger signal setting
the threshold PW plus the safety margin is detected by pacemaker
100. A delay timer is optionally started at block 754, and the
trigger signal is detected as a threshold search trigger signal at
block 756 for use in setting a PW. The PW is determined from the
trigger signal at block 758. At block 760, the PW stored in
pacemaker memory 210 is updated to the PW determined from this
final threshold search trigger signal, i.e., the threshold PW plus
the safety margin. A pacing pulse is delivered at the updated
stored PW at block 762 and 764. The ICD 14 may monitor the ECG
signal to verify that capture occurred in response to this pacing
pulse delivered at the updated PW.
[0195] Now operating in a therapy delivery mode, the ICD 14 starts
the AV interval at block 706 after sensing a P-wave at block 704.
In the therapy delivery mode, the AV interval is set at block 706
to an optimal interval for promoting synchrony between the heart
chambers. When the AV interval expires, the ICD 14 controls the
emitting device 18 to emit a short therapy trigger signal at block
708. The therapy trigger signal is delivered for a minimum duration
(signal width) that is reliably detectable by the pacemaker and
does not include pacing PW information.
[0196] At block 752, the pacemaker 100 detects the trigger signal
and starts the optional delay timer at block 754. At block 756, the
pacemaker control module 206 compares the duration of the trigger
detect signal 216 produced by the receiver 212 to a threshold
search interval. If the trigger detect signal 216 is determined to
be a "short" trigger, i.e., less than a threshold search interval,
the trigger signal is recognized as a pacing therapy trigger signal
and not a threshold search trigger signal. The pacemaker 100 does
not determine a PW from the trigger signal. The pacing pulse is
started at block 762, and a PW timer is started using the stored
PW, which was last updated based on the threshold PW determined
during the previous threshold search.
[0197] Upon expiration of the PW timer, the pacing pulse is
terminated at block 764. The pacing capacitor is recharged at block
750. The system continues to operate in the pacing therapy mode
(blocks 704 through 708 for the ICD 14 and blocks 750 through 756,
762 and 764 for the pacemaker 100) until it is time for the next
threshold search. During the pacing therapy mode, minimal energy is
used to generate the trigger signal, and the pacing pulses are
delivered with the PW that is stored in pacemaker memory 210
without determining a PW from the trigger signal on a beat-by-beat
basis. The trigger signal is transmitted with PW information only
during the threshold search mode (blocks 710 through 726 for the
ICD). Otherwise the trigger signal is a timing signal only, without
PW information, for the pacemaker 100 to use for delivering the
pacing pulse at the therapeutic AV interval.
[0198] FIG. 17 is a flow chart 800 of a method for providing a
pacemaker battery alert signal when the pacemaker battery reaches a
threshold voltage level. For example, an elective replacement
indicator (ERI) alert signal may be generated by ICD 14 when the
pacemaker battery voltage (of power source 214) falls below a
predetermined level. An ERI is a flag set by pacemaker 100 when the
pacemaker battery voltage falls below the predetermined level. An
ERI alert signal generated by ICD 14 notifies the patient and/or
clinician that pacemaker replacement is recommended to avoid the
pacemaker battery reaching end of life, causing a disruption in the
patient's therapy. Since pacemaker 100 may not have wireless RF
telemetry capability for transmitting an ERI alert to an external
programmer or other device, ICD 14 may be configured to detect an
ERI condition of pacemaker 100 and transmit the ERI alert signal to
an external device via telemetry module 88 to notify a clinician
and/or patient of the ERI condition.
[0199] In flow chart 800, operations and decisions enclosed by
dotted-line 803 represent functions performed by pacemaker 100.
Operations and decisions shown enclosed by dashed line 801
represent functions performed by ICD 14. Beginning with the
pacemaker operations 803, the pacemaker control module 206
determines if an ERI condition is detected at block 850. Pacemaker
control module 206 includes a battery monitor 218 for detecting a
battery voltage of power source 214 that is less than an ERI
voltage threshold. For example, the battery monitor 218 may include
a comparator for comparing the battery voltage to a predetermined
ERI threshold. The ERI threshold may be a fixed value or may be
based on a pacing history (e.g., frequency and PW) and an
estimation of remaining battery life based on the pacing history.
Reference is made to commonly-assigned U.S. Pat. No. 5,402,070
(Markowitz, et al.) and U.S. Pat. No. 6,016,448 (Busacker, et al.)
for descriptions of ERI determinations, both of which patents are
incorporated herein by reference in their entirety.
[0200] As long as an ERI condition is not detected at block 850,
the pacing pulse amplitude (PA) remains at a fixed, initial setting
that is referred to as a "LOW" setting at block 852 because it is
lower than the PA that will be used when an ERI condition is
detected. The fixed LOW setting may be a fixed percentage of the
battery voltage, e.g., 50% of the battery voltage. Alternatively,
the PA may be set at a fixed voltage, e.g. 1.5 V.
[0201] The pacemaker 100 charges the pacing capacitor between
pacing pulses at block 856 and discharges the capacitor in response
to detecting a trigger signal at block 858 to deliver a pacing
pulse at block 860. The pacing pulse is delivered after an optional
delay interval, using the LOW PA, and either a stored PW or a new
PW determined from the trigger signal as described in conjunction
with FIG. 16.
[0202] After delivering the pacing pulse, the pacemaker control
module 206 determines if it is time to check the battery voltage at
block 862 to detect an ERI condition. If not, the pulse generator
202 begins charging the capacitor(s) at block 856 to the LOW
PA.
[0203] If it is time to check the battery voltage, the control
module 206 performs an ERI analysis to detect an ERI condition at
block 850. If an ERI condition is detected, i.e., if the battery
voltage falls below an ERI voltage, the PA is set to a HIGH setting
at block 854. The "HIGH" setting is a setting that is greater than
the initial fixed PA setting used prior to the ERI condition. For
example, the "HIGH" setting may be a fixed voltage that is greater
than the LOW setting, e.g. 2.0 V. Alternatively, the HIGH setting
may be an increased percentage of the battery voltage, e.g. 100% of
the remaining battery voltage.
[0204] The pulse generator 202 charges the pacing capacitor(s) to
the HIGH PA voltage at block 856, and pacemaker 100 continues to
deliver pacing pulses in response to detected trigger signals at
blocks 858 and 860 according to the methods described above. When
the pacing PA is set to a HIGH setting, and the PW remains the
same, the pacemaker 100 delivers pacing pulses that are highly
likely to continue capturing the heart. The next time a pacing PW
capture threshold search is performed, as described in conjunction
with FIG. 16, the PW capture threshold will be lower due to the
HIGH PA. The PW will be adjusted to the shorter PW capture
threshold to avoid excessive battery drain. By increasing the PA
from the LOW to the HIGH setting, however, the ICD 14 is able to
detect the ERI condition and issue a pacemaker ERI alert as
described next.
[0205] Now referring to ICD operations 801, the ICD 14 monitors the
ECG for sensing P-waves at block 802 and starts an AV interval at
block 804 in response to a sensed P-wave. At block 806, the ICD 14
controls the emitting device 18 to send a trigger signal upon
expiration of the AV interval.
[0206] After sending the control signal 95 to cause trigger signal
transmission, the ICD 14 may monitor the ECG signal for a loss of
pacing capture (LOC) as indicated at decision block 808. LOC
monitoring may be performed on every paced beat, hourly, daily, or
other scheduled interval.
[0207] LOC may be detected by analyzing the ECG signal. For
example, if an R-wave is not detected within an expected time
interval from sending the trigger signal or after detecting the
pacing pulse signal on the ECG signal, LOC may be detected.
Additionally or alternatively, morphology analysis of the R-wave
sensed after the trigger signal may be performed to detect an
R-wave morphology that corresponds to an intrinsically conducted
depolarization instead of a pacing-induced R-wave, i.e., an evoked
response.
[0208] If LOC is detected, a pacing PW threshold search may be
performed at block 814 to detect an increase in PW threshold. The
PW stored in the pacemaker 100 is adjusted as needed based on the
pacing threshold search results by sending a trigger signal
containing PW information as described previously in conjunction
with FIG. 16.
[0209] If LOC is not detected, the ICD 14 is configured to monitor
the ECG signal at block 810 to detect a possible ERI condition of
pacemaker 100. The ECG signal may be monitored for an ERI condition
on a scheduled basis, for example every 24 hours or another time
interval. One possible ERI condition is an increase in the pacing
pulse signal amplitude present on the monitored ECG signal due to
an increase in the pacing PA to the HIGH PA setting by pacemaker
100. The ICD 14 may measure the amplitude of the pacing pulse
signal on the ECG signal and compare the amplitude to a previously
measured amplitude, averaged amplitude, or predefined amplitude
threshold. The ICD 14 can set a time window for measuring the
pacing pulse signal amplitude on the ECG signal since the ICD 14
controls the timing of the pacing pulse via the trigger signal.
[0210] If a threshold increase in the pacing pulse signal amplitude
on the ECG signal is detected by the ICD 14 at block 812, the
pacemaker 100 may have reached an ERI condition that caused the
pacemaker 100 to increase the pacing PA to the HIGH setting. The
ICD 14 may advance to block 814 to perform a pacing PW threshold
search as described in conjunction with FIG. 16.
[0211] If the PW capture threshold has decreased by a threshold
amount compared to one or more most recently determined PW
threshold(s), as determined at decision block 816, a pacemaker ERI
condition is confirmed at block 818. If the pacing PA has been
increased by the pacemaker 100, the PW required to achieve capture
will be decreased. The increased pacing PA determined from the ECG
signal (at block 812) and/or the decreased PW capture threshold
(determined at block 816) provide evidence that the pacemaker 100
has changed the pacing PA due to an ERI condition. A pacemaker ERI
alert signal is generated by the ICD 14 at block 818, which is
transmitted by the ICD RF telemetry communication module 88 to an
external device 40, such as a programmer or home monitor.
[0212] Alternatively, the ICD 14 may generate an ERI alert signal
at block 818 directly in response to detecting an increase in PA at
block 812 without verifying the ERI condition by performing a
threshold search. The ICD 14 may be configured to detect an ERI
condition by detecting a predetermined minimum number of
consecutive pacing pulses on the ECG signal each having a threshold
change in the pacing pulse signal amplitude compared to a
previously measured pacing pulse signal amplitude. For example, if
the ICD detects three consecutive pacing pulses on the ECG signal
each having a signal amplitude that is 50% (or another percentage)
greater than the pacing pulse signal amplitude measured on the
previous day, an ERI condition is detected.
[0213] In other examples, each time a pacing threshold search is
performed, the PW capture threshold may be compared to a previously
determined PW capture threshold. A sudden drop in PW capture
threshold is unexpected and may indicate a PA increase by the
pacemaker due to an ERI condition. For example, without limitation,
if a decrease in PW capture threshold of more than 25% since the
previous pacing threshold search has occurred, a sudden drop in PW
capture threshold is detected. If a sudden drop in PW capture
threshold is detected, the pacemaker ERI alert is produced at block
818 without necessarily detecting the pacing pulse PA at block
812.
[0214] FIG. 18 is a flow chart 900 of a method for controlling a
triggered pacemaker using less than a 1:1 rate ratio of trigger
signals to pacing pulses. In some applications, a stimulation pulse
may be synchronized to frequently sensed events, which would
require frequent trigger signals and significant power consumption
by the emitting device. For example, in CRT, an LV pacing pulse is
delivered on every cardiac cycle, e.g., after every sensed P-wave,
in order to improve ventricular synchrony. In order to reduce power
consumption for triggering an intracardiac pacemaker on every
cardiac cycle, more than one pacing pulse may be delivered in
response to one trigger signal resulting in a ratio of trigger
signals to pacing pulses that is less than a 1:1 ratio. In other
words the trigger signal rate is less than the rate of delivered
pacing pulses over the same interval of time.
[0215] In flow chart 900, the operations in dashed box 901
represent functionality of the ICD 14 (or other sensing device).
Operations shown in dotted box 903 represent functionality of the
pacemaker 100. The methods described in conjunction with flow chart
900 may be implemented during periods of time that the patient's
heart rate is expected to remain relatively steady, for example
during sleep or during low levels of activity. As such, the
techniques for controlling pacing using fewer trigger signals than
delivered pacing pulses may be enabled during particular times of
day, in response to a patient activity signal and/or posture
signal, or other indication that the heart rate is likely to remain
relatively stable.
[0216] At block 902, the ICD senses a P-wave. The AV interval timer
is started at block 904 in response to sensing the P-wave. A PP
interval (PPI) is determined at block 906 as the interval of time
between the sensed P-wave and the immediately preceding sensed
P-wave. The PPI is used in determining an interval change metric at
block 908. When the heart rate (HR) is stable, the pacemaker 100
may deliver pacing pulses at a repeated, fixed interval of time
without requiring a new trigger signal. For example, if the HR is
60 bpm (equivalent to a stable 1000 ms PPI), two consecutive
trigger signals delivered at an 80 ms AV interval from each of two
consecutively sensed P-waves will be delivered 1000 ms apart. The
pacemaker 100 may determine the time interval between two
consecutive trigger signals and store this as a trigger interval
for automatically delivering a series of pacing pulses at the
trigger interval in response to the two trigger signals. If no new
trigger signal is detected before the stored trigger interval
expires, the pacemaker 100 may automatically deliver a pacing pulse
at the stored trigger signal interval, which is 1000 ms in the
current example. As long as the HR remains steady at 60 bpm, the LV
pacing pulses delivered spaced apart in time by the trigger
interval will be delivered at the targeted AV interval during each
cardiac cycle without requiring a trigger signal during each
cardiac cycle.
[0217] If the HR changes, however, a stored trigger signal interval
may result in an actual AV interval to be unacceptably different
than the targeted AV interval. As HR changes, therefore, a new
trigger signal needs to be sent by the emitting device 18 to
correct the pacemaker timing and cause the LV pacing pulse to be
delivered at the target AV interval or within an acceptable range
of the AV interval.
[0218] Accordingly, after sensing the P-wave at block 902 and
measuring the current PPI at block 906, the ICD 14 assesses one or
more recently measured PPIs. The ICD 14 determines if a change in
the PPI is leading to unacceptable timing of the pacing pulse. An
actual AV interval between the sensed P-wave and an imminent pacing
pulse that will be delivered by the pacemaker 100 at a stored
trigger interval may be outside an acceptable range of the target
AV interval.
[0219] At block 908, the ICD 14 determines an interval change
metric (ICM) using the current PPI. The ICM may be a difference
between the current PPI and one or more previous PPIs, an
accumulated (summed) difference between consecutive PPIs, a trend
of PPI differences, or other index computed from the measured PPI
and one or more preceding PPIs. It is recognized that in
alternative embodiments, the ICD 14 may determine RR intervals and
determine an interval change metric from the RR intervals.
[0220] The ICM is compared to a change threshold at block 910. If
the ICM is greater than a change threshold, LV pacing at the
trigger interval presently stored in the pacemaker 100 will result
in a pacing pulse delivered at an actual AV interval unacceptably
different than the targeted AV interval. If the ICM is greater than
the change threshold, therefore, the ICD 14 controls the emitting
device 18 to send a trigger signal at block 914 upon expiration of
the AV interval. In some examples, the AV interval timer may be
started after determining that a trigger signal is needed based
upon the ICM. For example, when the ICM exceeds the change
threshold, an AV interval timer may be started on the next sensed
P-wave to produce a trigger signal on the next cardiac cycle.
[0221] A counter P is reset to zero at block 916 after sending a
trigger signal. The counter P is used to count the number of
P-waves that are sensed without sending a trigger signal. As
described below, the pacemaker 100 may include a lockout safety
feature that limits the number of pacing pulses delivered at a
stored trigger interval without receiving a trigger signal. Pacing
pulses delivered at a stored trigger interval when a trigger signal
is not detected are referred to as "non-triggered" pacing pulses.
If a maximum number of non-triggered pacing pulses are delivered,
the pacemaker 100 stops delivering pacing pulses until a new
trigger signal is detected. Non-triggered pacing pulses are
therefore counted by the pacemaker 100, and the ICD 14 counts
sensed P-waves for which no trigger is sent to track the number of
non-triggered pacing pulses. The P counter that is reset at block
916 is therefore a counter that tracks the number of times that the
pacemaker 100 has likely delivered a non-triggered pacing pulse
using a stored trigger interval but no trigger signal was sent by
the emitting device 18. Since a trigger signal is sent at block
914, any count stored by the P counter is cleared and reset to
zero.
[0222] At block 918, the ICD controls the emitting device to send
at least one more trigger signal following the next consecutive
P-wave in order to deliver at least two consecutive trigger signals
(at blocks 914 and 918) that are used by the pacemaker 100 to
update the stored trigger interval. Two consecutive trigger signals
sent at an AV interval following two consecutive sensed P-waves
establish a trigger interval that matches the HR of the current
cardiac cycle. This single pair of trigger signals may be used by
the pacemaker 100 to update the stored trigger interval.
[0223] Alternatively, the ICD 14 may deliver trigger signals at AV
intervals following more than two consecutively sensed P-waves such
that two or more consecutive trigger intervals are determined by
the pacemaker 100 to establish a new trigger interval matching the
patient's current heart rate and storing an updated trigger
interval. The number of consecutive trigger signals sent by the ICD
14 to establish an updated trigger interval in the pacemaker 100
may be a predetermined fixed number or may be automatically
adjusted based on the variability of the HR.
[0224] After sending a required number of consecutive trigger
signals at block 918, the time interval between the sent trigger
signals is stored in the ICD memory 82 at block 920. The time
interval may be a single trigger interval or an average of two or
more trigger intervals. The time interval stored by the ICD 14
matches the updated trigger interval stored by the pacemaker 100
after detecting the consecutive trigger signals sent to the
pacemaker 100 at blocks 914 and 918. The stored trigger interval in
the ICD 14 and the stored trigger interval in the pacemaker 100
will match each other and the patient's current HR within an
acceptable error. In some examples, the ICD 14 may use the stored
trigger interval to determine the interval change metric and/or if
the interval change metric exceeds a change threshold that would
result in unacceptable timing of a non-triggered pacing pulse.
[0225] The ICD 14 returns to sensing P-waves at block 902 and
monitoring the ICM for determining when a trigger signal is again
needed to correct the timing of an imminent pacing pulse delivered
by the pacemaker 100. If the ICM does not exceed the change
threshold at decision block 910, the P counter is compared to the
maximum number of allowable non-triggered pacing pulses at block
930. If the non-triggered pacing count is within a predetermined
limit from the maximum allowable number of non-triggered pacing
pulses, for example one less than the maximum allowable
non-triggered pacing pulses, the AV interval started at block 904
is allowed to expire. The ICD 14 controls the emitting device 18 to
send a trigger signal at block 914.
[0226] The trigger signal is sent even though the interval change
metric has not reached the change threshold. The trigger signal is
sent to prevent the pacemaker 100 from reaching a lockout number of
non-triggered pacing pulses. A single trigger signal may be sent to
the pacemaker 100 to reset the non-triggered pacing pulse count at
block 916 and an analogous counter in the pacemaker 100, without
updating the stored trigger interval. The ICD 14 may optionally
advance to block 918 to send one or more additional triggers to
update the stored trigger interval.
[0227] In some examples, a single trigger signal is sent when the
ICM threshold has not been reached (block 910) but the number of
consecutive non-triggered pacing pulses is reaching a maximum
lockout number (block 930). Since the trigger interval stored by
the pacemaker 100 may still be valid, the pacemaker 100 may ignore
the single trigger signal for updating the stored trigger interval.
The single trigger signal is more than one cardiac cycle since the
last trigger signal and may be more than one cardiac cycle until
the next trigger signal. The single trigger signal, therefore, is
not indicative of a valid trigger interval and is not used in
updating the stored trigger interval. The single trigger signal may
be used to confirm that the stored trigger interval is still valid.
As such, when a single trigger signal is used to prevent pacemaker
lockout, the single trigger signal may have a different
characteristic than trigger signals used to establish a new,
updated trigger interval. The amplitude, signal width, signal
frequency, pulse number, pulse interval or other aspect of the
single trigger signal may be set differently than trigger signals
used to update the stored trigger interval when the ICM threshold
has been reached.
[0228] For example, when a series of trigger signals are being sent
to update the trigger interval in response to the ICM threshold
being reached, the first trigger signal sent at block 914 may be
sent with a relatively longer signal width than the subsequent
trigger signals sent at block 918 and longer than a single trigger
signal that is sent to prevent lockout. Alternatively, the single
trigger signal sent to prevent lockout may have a relatively longer
signal width than the trigger signals sent for updating the trigger
interval. The pacemaker 100 is configured to detect the different
trigger signals to respond appropriately by either updating a
stored trigger interval or leaving the stored trigger interval the
same.
[0229] If the non-triggered pacing pulse count P has not reached
the maximum lockout number (or is not within a predetermined range
of the maximum lockout number) as determined at decision block 930,
the AV interval timer is stopped at block 932 and no trigger signal
is sent. The non-triggered pacing pulse count (P count) is
increased by one at block 934. The ICD 14 returns to block 902 to
sense the next P-wave.
[0230] Now referring to the pacemaker functions shown in dotted
block 903, the pacemaker 100 charges the pacing capacitor(s) at
block 952 after delivering a preceding pacing pulse, while waiting
for the next trigger signal. If a trigger signal is detected at
block 954, an optional delay timer is started at block 956. Pacing
capacitor charging may continue during the delay time as
needed.
[0231] A counter in the pacemaker control module 206 counts the
number of non-triggered pacing pulses that have been delivered
consecutively. At block 958, the non-triggered pace count is reset
to zero in response to the detected trigger signal at block 954
since the next pacing pulse will be a triggered pacing pulse. The
non-triggered pace count is used to lockout pacing as a safety
feature if a maximum number of non-triggered pacing pulses have
been reached as described above.
[0232] Another counter in the pacemaker control module 206 may
count the number of consecutive triggered pacing pulses. The
triggered pace count is increased by one at block 960. The
triggered pace count may be used to determine when the trigger
interval should be updated using the current trigger signal and one
or more previous trigger signals.
[0233] Upon expiration of the delay timer, a pacing pulse is
delivered at block 962. The pacing pulse may be delivered using a
fixed PA and a PW stored in pacemaker memory 210 or determined from
the trigger signal using any of the methods described above, e.g.,
in conjunction with FIGS. 11 through 15. If the triggered pace
count is greater than one, as determined at block 964, the stored
trigger interval is updated at block 966. For example, if at least
two consecutive trigger signals have been received, without an
intervening non-triggered pacing pulse, the time interval between
the two detected trigger signals is determined by a timer in the
pacemaker control module 206. The determined trigger interval is
stored as an updated trigger interval at block 966. As described
above, two or more consecutive trigger signals may be delivered for
use by the pacemaker 100 for updating the trigger interval. When
the required number of consecutive trigger signals have been
detected, the pacemaker 100 uses the intervals measured between the
trigger signals to determine an updated trigger interval at block
966.
[0234] As indicated above, the trigger signals that are to be used
by the pacemaker 100 for updating the stored trigger interval may
be designated by a different signal feature recognizable by the
pacemaker 100, based on an analysis of the trigger signal by TS
analysis module 220. At block 968, a timer in pacemaker control
module 206 is set to the updated trigger interval and started. The
process returns to block 952 to recharge the pacing capacitor
during the trigger interval.
[0235] During the trigger interval, the pacemaker 100 waits for the
next trigger signal at block 954. If the trigger interval expires
before detecting a trigger signal, as indicated at block 980, the
triggered pace count is reset to zero at block 986. The
non-triggered pace count is increased by one at block 988. The
non-triggered pacing pulse is delivered at block 962. Since the
triggered pace count has been reset to zero (block 986), the stored
trigger interval will not be updated (negative decision at block
964). The non-triggered pace count is compared to a lockout number,
N, at block 990. If the lockout number N has not been reached, the
control module 206 starts a timer set to the previously stored
trigger interval at block 968. Up to N non-triggered pacing pulses
may be delivered at the stored trigger interval if no new trigger
signal is detected.
[0236] If the lockout number N is reached, pacing pulse delivery is
suspended at block 992. Pacing delivery may be locked until a new
trigger signal is detected (by returning to block 954) to confirm
the currently stored trigger interval is still valid, or the new
trigger signal is used with at least one more trigger signal for
updating the stored trigger interval.
[0237] It is understood that the sequence of operations shown in
flow chart 900 and other flow charts presented herein may be
performed in a different order than the order of the blocks as
shown. In some cases operations may be performed substantially
simultaneously, such as adjusting counters and setting timers. For
example, blocks 956, 958 and 960 may be performed simultaneously
upon detecting the trigger signal at block 954. The operations
shown in the flow charts presented herein may be combined in other
combinations than those shown and in some examples some operations
may be omitted or added.
[0238] FIG. 19 is a timing diagram 1000 depicting one method for
determining an interval change metric and controlling pacing pulses
delivered by a triggered pacemaker. The ICD 14 (or other sensing
device) senses P-waves (PS) 1002, 1004, 1006, and 1008. The sensed
P-waves 1002 and 1004 initially arrive at a steady heart rate
having a PPI 1010 matching a stored trigger interval (STI). The
stored trigger interval 1010 is the trigger interval stored by the
ICD 14 and is expected to match the trigger interval (TI) 1030
stored by the pacemaker 100.
[0239] In one embodiment, the ICD 14 determines a difference
between the STI and each of the PPIs 1010, 1012 and 1014 measured
between two consecutively sensed P-waves 1002 through 1008.
Consecutive differences between measured PPIs and the STI are
summed to accumulate differences between the PPIs and the STI. The
interval change metric (ICM) may be determined by the ICD 14 as the
summation of the PPI-STI differences determined for each PPI since
the last trigger signal.
[0240] In the example shown in FIG. 19, the first PPI-STI interval
difference is 0 ms. The HR is initially steady. The ICM has a value
of 0 ms after sensing P-wave 1004. The ICD 14 does not deliver a
trigger signal. The trigger interval (TI) 1030 stored by the
pacemaker 100 expires without detecting a trigger signal. An LV
pacing pulse (VP) 1022 is delivered by the pacemaker 100 at the TI
1030 following the previous VP 1020. The actual AV interval 1032
between PS 1004 and VP 1022 is equal to a targeted AV interval
since the sensed P-wave 1004 occurs at the STI.
[0241] The next sensed P-wave 1006 occurs at a PPI 1012 that is X
ms shorter, e.g. 6 ms shorter, than the STI. The ICM is set equal
to the sum of the previous ICM (0 ms) and the current PPI-STI
difference. The ICM, therefore, equals -6 ms after PS 1006. The ICD
14 compares the ICM to a change threshold after each sensed P-wave
1002, 1004, 1006 and 1008. If the ICM is less than the threshold,
no trigger signal is sent. In this illustrative example, the change
threshold is set at .+-.10 ms. Since the ICM is -6 ms after PS
1006, no trigger signal is sent.
[0242] The next LV pacing pulse 1024 is delivered after the
previous VP 1022 at the TI 1030 stored by the pacemaker 100. The VP
1024 delivered at the TI 1030 results in an actual AV interval 1034
that is 6 ms longer than the targeted AV interval due to the P-wave
1006 arriving 6 ms earlier than the STI. This fluctuation of the
actual AV interval within .+-.10 ms of the targeted AV interval is
considered acceptable.
[0243] The next sensed P-wave 1008 occurs at a PPI 1014 equal to
the previous PPI 1012, e.g. 6 ms shorter than the STI. The ICM is
updated by summing this difference with the previous ICM. As such,
after PS 1008, the ICM is -12 ms (ICM=0 ms-6 ms-6 ms). The ICM now
exceeds the change threshold of .+-.10 ms. The ICD 14 controls the
emitting device to emit a trigger signal 1015 at the target AV
interval 1040 (less any system delays) following the sensed P-wave
1008. The trigger signal 1015 causes the pacemaker 100 to deliver a
pacing pulse 1026 at an actual AV interval 1036 equal to the target
AV interval 1040.
[0244] Without this correction to the VP 1026 timing made by
controlling emitting device 18 to emit trigger signal 1015, a
hypothetical VP 1028 that would have been delivered at the
expiration of the stored TI 1030 would occur at an unacceptably
long AV interval 1038, 12 ms longer than the targeted AV interval
1040. The detected trigger signal 1015 and the next trigger signal
(not shown) may be used by the pacemaker 100 to reset the TI
1030.
[0245] FIG. 20 is a timing diagram 1050 illustrating an example
method for controlling triggered and non-triggered pacing pulses
using a delay time. The ICD 14 senses P-waves 1052, 1054, 1056 and
1058 occurring at respective PPIs 1053, 1055 and 1057 during a
steady, stable HR. The ICD 14 controls the emitting device 18 to
emit a trigger signal 1064 at a control time interval 1062 after
sensing P-wave 1052. The pacemaker 100 detects the trigger signal
1064 and produces a trigger detect (TD) signal 1066. The pacemaker
100 starts a delay time 1080 upon detecting the trigger signal 1064
and delivers the triggered pacing pulse VP 1070 upon expiration of
delay time 1080. The control time interval 1062 used by the ICD 14
for controlling the time of the emitted trigger signal 1064 after
PS 1052 is equal to the targeted AV interval 1060 minus delay time
1080 (and any system delays).
[0246] On the next sensed P-wave 1054, the PPI 1053 is determined.
The control time 1062 is started. A trigger signal 1064 is emitted
at the expiration of control time 1062. A trigger detect signal
1068 is produced by the pacemaker 100, which starts delay time
1080. The triggered VP 1072 is delivered at the target AV interval
1060 upon expiration of delay time 1080.
[0247] The pacemaker 100 determines a trigger detect time interval
(TDTI) 1078 between the two consecutive TD signals 1066 and 1068.
The pacemaker 100 updates the trigger interval (TI) 1082 stored by
the pacemaker 100 using the TDTI 1078. Assuming that the HR has
been stable for a required number of PPIs to establish an updated,
stored trigger interval, the updated trigger interval (TI) 1082 is
started upon the next triggered VP 1072, which is delivered after
the delay time 1080.
[0248] As described above, the ICD 14 determines a stored trigger
interval (STI) as the interval between emitted trigger signals
1064, which is expected to match the updated trigger interval 1082
stored by the pacemaker 100. When the ICD 14 senses the next P-wave
1056, the PPI 1055 is determined and compared to the STI. PPI 1055
equals the STI. The ICD 14 determines that a trigger signal is not
needed following PS 1056 since the PPI 1055 equals the STI. If no
trigger signal is detected by the pacemaker 100 before expiration
of the TI 1082, a VP 1074 is delivered at the expiration of the TI
1082. VP 1074 is properly delivered at the target AV interval 1060
using the TI 1082 without requiring emission and detection of a
trigger signal following PS 1056.
[0249] A next TI 1084 is started upon the VP 1074. This process
repeats on the next PS 1058, which occurs at a PPI 1057 equal to
the STI. No trigger signal is delivered. When the TI 1084 expires
without detecting a trigger signal, the next VP 1076 is delivered
at the target AV interval 1060, and another TI (not shown) is
started.
[0250] If a trigger signal is detected before the TI 1082 or 1084
expires, the delay time 1080 would be started, and the VP would be
delivered at the end of the delay time. A newly detected trigger
signal would be used to update the stored TI. However, as long as
the HR remains steady, the ventricular pacing pulses can be
delivered at the targeted AV interval 1060, or within a predefined
acceptable range of the AV interval 1060, without requiring a
trigger signal on every heartbeat. As described in conjunction with
FIG. 19, the ICD 14 monitors an ICM. If the HR increases so that
the ICM exceeds the ICM threshold, the ICD 14 controls the emitting
device 18 to deliver a trigger signal to update the trigger
interval stored by the pacemaker 100.
[0251] FIG. 21 is a timing diagram 1100 depicting an example method
for determining an ICM and controlling pacing pulses delivered by a
triggered pacemaker 100 during a decreasing HR. The time intervals
shown in FIG. 21, and other timing diagrams presented herein, are
illustrative in nature and are not necessarily drawn to scale. In
the example shown in FIG. 19, a trigger signal can be sent to the
pacemaker 100 during any cardiac cycle at a shorter interval than a
previous trigger interval to cause the pacemaker 100 to deliver a
pacing pulse earlier when the HR increases (PPIs shorten). When the
HR slows down, however, a trigger signal may need to be delivered
later than the expiration of a trigger interval that was previously
updated during a relatively faster HR. By sending a trigger signal
before the end of a targeted AV interval, and including a delay
time 1080 as shown in FIG. 20, a trigger signal can be sent to the
pacemaker 100 before the expiration of a trigger interval and a
scheduled non-triggered pacing pulse to cause control module to
start a delay timer to slow down the rate of the pacing pulses. An
illustrative example of this situation is shown in FIG. 21.
[0252] In FIG. 21, the ICD 14 (or other sensing device) senses
P-waves (PS) 1102, 1104, 1106, and 1108. The sensed P-waves 1102
and 1104 initially arrive at a steady heart rate having a PPI 1110
matching a stored trigger interval (STI). The stored trigger
interval is the trigger time interval stored by the ICD 14 that is
expected to match the TI 1130 stored by the pacemaker 100 as
described above.
[0253] The ICD 14 determines the ICM as the summation of the
consecutive PPI-STI differences when no trigger signal is
delivered. The ICM represents an accumulation of cardiac cycle
length differences since a most recent trigger signal was delivered
to update a trigger interval stored by the pacemaker 100. In the
example shown in FIG. 21, the first PPI-STI interval difference is
0 ms due to a steady HR. The ICM has a value of 0 ms after sensing
P-wave 1104. The ICD 14 does not deliver a trigger signal. An LV
pacing pulse (VP) 1122 is delivered by the pacemaker 100 at the
expiration of the TI 1130 started upon the previous VP 1120. The
actual AV interval 1132 between PS 1104 and VP 1122 matches a
targeted AV interval 1160 since PS 1104 occurs at the STI.
Non-triggered VP 1120 and non-triggered VP 1122 each occur at the
target AV interval 1160 without requiring a trigger signal after PS
1102 and PS 1104 as long as the HR remains steady.
[0254] The next sensed P-wave 1106 occurs at a PPI 1112 that is 6
ms longer than the STI. The ICM is set equal to the sum of the
previous ICM (0 ms) and the current PPI-STI difference (+6 ms). The
ICM equals +6 ms after PS 1106. The ICD 14 compares the ICM to the
change threshold of .+-.10 ms in this example. Since the ICM is
less than the change threshold, no trigger signal is sent.
[0255] The TI 1130' started at the expiration of the previous VP
1122 expires and the next VP 1124 is delivered. VP 1124 is a
non-triggered pacing pulse delivered at an actual AV interval 1134
based on the TI 1130 stored by the pacemaker 100. The actual AV
interval 1134 is 6 ms shorter than the targeted AV interval due to
the P-wave 1106 arriving 6 ms later than the STI. This fluctuation
of the actual AV interval within .+-.10 ms of the targeted AV
interval 1160 is within acceptable limits.
[0256] The next sensed P-wave 1108 occurs at a PPI 1114 equal to
the previous PPI 1112, i.e. 6 ms longer than the STI. The ICM is
updated by summing this difference with the previous ICM. As such,
after PS 1108, the ICM is +12 ms (ICM=0 ms+6 ms+6 ms). The ICM now
exceeds the change threshold of .+-.10 ms. The ICD 14 controls the
emitting device 18 to emit a trigger signal 1115 at a control time
interval 1162 following the sensed P-wave 1108. Control time
interval 1162 is equal to the target AV delay 1160 minus a delay
time 1140 applied by the pacemaker 100 after detecting a trigger
signal (less any system delays).
[0257] The trigger signal 1115 is detected by the pacemaker 100
during TI 1130''. The pacemaker 100 produces a TD signal 1128 in
response to the trigger signal 1115, before a scheduled
non-triggered pacing pulse 1150. The non-triggered pacing pulse
1150 is withheld. The TD signal 1128 starts delay time 1140. A
scheduled non-triggered pacing pulse 1150 at the expiration of the
TI 1130'' would arrive at a hypothetical AV interval 1136, which is
unacceptably shorter than the target AV interval 1160. By
delivering trigger signal 1115 during the TI 1130'' and starting a
delay time 1140 in response to the trigger signal, the VP 1126 is
delivered later than expiration of the TI 1130''. The actual AV
interval 1138 is equal to the target AV interval 1160. The control
time 1162 and the delay time 1140 (plus any system delays accounted
for in setting control time 1162 and delay time 1140') result in
the triggered VP 1126 at the target AV interval 1160. Additional
trigger signals may be delivered on subsequently sensed P-waves to
reset the TI stored by the pacemaker 100.
[0258] Thus, various examples of a medical device system and
associated method for controlling a triggered therapy delivery
device have been described according to illustrative embodiments.
However, one of ordinary skill in the art will appreciate that
various modifications may be made to the described embodiments
without departing from the scope of the following claims.
* * * * *